class.php
<?php
class class1 {
var $a;
function class1($data) {
$this->a = $data;
}
}

?>

a.php
<?php

require_once('class.php');

session_start();
$_SESSION['a'] = new class1(5);
echo '<a href="b.php">b</a>';
?>

b.php

<?php
require_once('class.php');
session_start();
echo '<pre>';
var_dump($_SESSION['a']);
var_dump($_SESSION['a']->a);
?>