diff --git a/yaserde/tests/serializer.rs b/yaserde/tests/serializer.rs
index 66480e0..eeb9c54 100644
--- a/yaserde/tests/serializer.rs
+++ b/yaserde/tests/serializer.rs
@@ -11,7 +11,15 @@ use yaserde::YaSerialize;
 macro_rules! convert_and_validate {
   ($model: expr, $content: expr) => {
     let data: Result<String, String> = to_string(&$model);
-    assert_eq!(data, Ok(String::from($content)));
+    assert_eq!(
+      data,
+      Ok(
+        String::from($content)
+          .split("\n")
+          .map(|s| s.trim())
+          .collect::<String>()
+      )
+    );
   };
 }
 
@@ -489,3 +497,87 @@ fn ser_custom() {
   let content = "<?xml version=\"1.0\" encoding=\"utf-8\"?><Date><Year>2020</Year><Month>1</Month><DoubleDay>10</DoubleDay></Date>";
   convert_and_validate!(model, content);
 }
+
+#[test]
+fn ser_flatten() {
+  #[derive(Default, PartialEq, Debug, YaSerialize)]
+  struct DateTime {
+    #[yaserde(flatten)]
+    date: Date,
+    time: String,
+    #[yaserde(flatten)]
+    kind: DateKind,
+  }
+
+  #[derive(Default, PartialEq, Debug, YaSerialize)]
+  struct Date {
+    year: i32,
+    month: i32,
+    day: i32,
+    #[yaserde(flatten)]
+    extra: Extra,
+    #[yaserde(flatten)]
+    optional_extra: Option<OptionalExtra>,
+  }
+
+  #[derive(Default, PartialEq, Debug, YaSerialize)]
+  pub struct Extra {
+    week: i32,
+    century: i32,
+  }
+
+  #[derive(Default, PartialEq, Debug, YaSerialize)]
+  pub struct OptionalExtra {
+    lunar_day: i32,
+  }
+
+  #[derive(PartialEq, Debug, YaSerialize)]
+  pub enum DateKind {
+    #[yaserde(rename = "holidays")]
+    Holidays(Vec<String>),
+    #[yaserde(rename = "working")]
+    Working,
+  }
+
+  impl Default for DateKind {
+    fn default() -> Self {
+      DateKind::Working
+    }
+  };
+
+  let model = DateTime {
+    date: Date {
+      year: 2020,
+      month: 1,
+      day: 1,
+      extra: Extra {
+        week: 1,
+        century: 21,
+      },
+      optional_extra: Some(OptionalExtra { lunar_day: 1 }),
+    },
+    time: "10:40:03".to_string(),
+    kind: DateKind::Holidays(vec![
+      "New Year's Day".into(),
+      "Novy God Day".into(),
+      "Polar Bear Swim Day".into(),
+    ]),
+  };
+
+  let content = r#"
+    <?xml version="1.0" encoding="utf-8"?>
+    <DateTime>
+      <year>2020</year>
+      <month>1</month>
+      <day>1</day>
+      <week>1</week>
+      <century>21</century>
+      <lunar_day>1</lunar_day>
+      <time>10:40:03</time>
+      <holidays>New Year's Day</holidays>
+      <holidays>Novy God Day</holidays>
+      <holidays>Polar Bear Swim Day</holidays>
+    </DateTime>"#;
+
+  convert_and_validate!(model, content);
+}
diff --git a/yaserde_derive/src/ser/expand_struct.rs b/yaserde_derive/src/ser/expand_struct.rs
index 0ecd409..ed208d4 100644
--- a/yaserde_derive/src/ser/expand_struct.rs
+++ b/yaserde_derive/src/ser/expand_struct.rs
@@ -327,19 +327,37 @@ pub fn serialize(
               })
             }
           }
-          FieldType::FieldTypeStruct { .. } => Some(quote! {
-            if let Some(ref item) = &self.#label {
-              writer.set_start_event_name(Some(#label_name.to_string()));
-              writer.set_skip_start_end(false);
-              item.serialize(writer)?;
+          FieldType::FieldTypeStruct { .. } => Some(if field_attrs.flatten {
+            quote! {
+              if let Some(ref item) = &self.#label {
+                writer.set_start_event_name(None);
+                writer.set_skip_start_end(true);
+                item.serialize(writer)?;
+              }
+            }
+          } else {
+            quote! {
+              if let Some(ref item) = &self.#label {
+                writer.set_start_event_name(Some(#label_name.to_string()));
+                writer.set_skip_start_end(false);
+                item.serialize(writer)?;
+              }
             }
           }),
           _ => unimplemented!(),
         },
-        FieldType::FieldTypeStruct { .. } => Some(quote! {
-          writer.set_start_event_name(Some(#label_name.to_string()));
-          writer.set_skip_start_end(false);
-          self.#label.serialize(writer)?;
+        FieldType::FieldTypeStruct { .. } => Some(if field_attrs.flatten {
+          quote! {
+            writer.set_start_event_name(None);
+            writer.set_skip_start_end(true);
+            self.#label.serialize(writer)?;
+          }
+        } else {
+          quote! {
+            writer.set_start_event_name(Some(#label_name.to_string()));
+            writer.set_skip_start_end(false);
+            self.#label.serialize(writer)?;
+          }
         }),
         FieldType::FieldTypeVec { data_type } => match *data_type {
           FieldType::FieldTypeString => {