The difference between synchronous and asynchronous postback is thatAsynchronous postback renders only the required part of the page and whereas, synchronous postback renders the entire page for any postback.Asynchronous postback executes only one postback at a time, that is, if you have two buttons doing asynchronous postback, the actions will be performed one by one; whereas, synchronous postback executes all the actions at once.Asynchronous postback only modifies the update panel that raises the postback; whereas, synchronous postback modifies the entire page.