First of all you should execute this code :<?php session_start(); $_SESSION["A"] = "Some Value";?>then you should execute this one : <?php start_session(); $_SESSION["A"] = "Some New Value"; // set new value session_reset(); // old session value restored echo $_SESSION["A"]; //Output: Some Value?>That is because session_reset() is rolling back changes to the last saved session data, which is their values right after the session_start().