diff --git a/querystring2body.go b/querystring2body.go
index 18b5375..17669f8 100644
--- a/querystring2body.go
+++ b/querystring2body.go
@@ -10,14 +10,21 @@ import (
 	"github.com/google/martian/parse"
 )
 
+const (
+	_contentType_applicationJSON = "appliction/json"
+	_contentTypeHeader           = "Content-Type"
+)
+
 type (
 	QueryModifierConfig struct {
 		KeysToExtract []string `json:"keys_to_extract"`
 		Template      string   `json:"template"`
+		ContentType   string   `json:"content_type"`
 	}
 	Query2BodyModifier struct {
 		keysToExtract []string
 		template      *template.Template
+		ContentType   string
 	}
 )
 
@@ -35,6 +42,7 @@ func queryModifierFromJSON(b []byte) (*parse.Result, error) {
 	mod := &Query2BodyModifier{
 		keysToExtract: cfg.KeysToExtract,
 		template:      tmpl,
+		ContentType:   cfg.ContentType,
 	}
 	return parse.NewResult(mod, []parse.ModifierType{parse.Request})
 }
@@ -54,5 +62,15 @@ func (m *Query2BodyModifier) ModifyRequest(req *http.Request) error {
 	req.ContentLength = int64(buf.Len())
 	req.Body = ioutil.NopCloser(buf)
 	req.URL.RawQuery = query.Encode()
+
+	if m.ContentType == "" && req.Header.Get("Content-Type") == "" {
+		// set default content-type header as application/json
+		req.Header.Set(_contentTypeHeader, _contentType_applicationJSON)
+	}
+
+	if m.ContentType != "" {
+		req.Header.Del(_contentTypeHeader)
+		req.Header.Set(_contentTypeHeader, m.ContentType)
+	}
 	return nil
 }