Provided are a cap assembly for a secondary battery. The cap assembly includes a cap-up, a PTC thermistor disposed under the cap-up, a vent disposed under the PTC thermistor, and an insulating plate disposed between the vent and the cap-up and preventing contact between the vent and the PTC thermistor. Here, the vent includes a curling part bent to cover an external surface of the insulating plate. Further, the secondary battery includes an electrode assembly, a can accommodating the electrode assembly and having an opening, and the cap assembly which seals the can.