A continuous variable valve duration system may include a camshaft, a first cam portion including a first cam, of which the camshaft is inserted therein, an internal bracket transmitting rotation of the camshaft to the first cam portion, a control shaft parallel to the camshaft, a slider housing in which the internal bracket is rotatably inserted, on which a control groove where the control shaft is inserted into is formed, and the slider housing movable vertical to the camshaft, a guider configured for guiding movement of the slider housing, a rocker shaft, a first rocker arm rotatably disposed to the rocker shaft of which a first end portion contacts with the first cam and of which a second end portion is connected to a first valve and a control portion selectively rotating the control shaft for changing a position of the slider housing.