sotik,
var obj = '{"success":1, "return":{"46081993":{"pair":"btc_rur", "type":"sell", "amount":0.01, "rate":15500, "order_id":425714310, "is_your_order":1, "timestamp":1414332926},"46061625":{"pair":"eur_rur", "type":"buy", "amount":0.1, "rate":53.242, "order_id":424877913, "is_your_order":1, "timestamp":1414264805}}}';
var data = eval("(" + obj + ")");
alert(data['return']['46081993'].amount)