To set the alignment for the second paragraph only, we apply the format to the first character in the second paragraph, which resides at index 23:
package{ import flash.display.Sprite; import flash.text.*; public class Main extends Sprite{ public function Main(){ var t:TextField = new TextField( ); t.width = 300; t.border = true; t.text = "This is paragraph one.\nThis is paragraph two."; var alignFormat:TextFormat = new TextFormat( ); alignFormat.align = TextFormatAlign.CENTER; t.setTextFormat(alignFormat, 23); addChild(t); } } }