A car top bicycle frame for retaining at least one bicycle transversally and obliquely comprises at least one positioning rod; a retaining buckle set; and a track set. By the positioning rod to combine to the track by the clamping sets, a bicycle can be installed upon a top of a car transversally and obliquely so as to be carried safely and conveniently. The bicycle can be fixed to the bicycle retaining frame on the ground before lifted to the car top. Then the bicycle and the frame are lifted to the entrance of the assisting guide track to enter into the track. The height for operation is reduced greatly so that no platform is needed. Only one people can lift the bicycle to the car top or descend the bicycle from the car top. More bicycles can be installed to the car top. The number of bicycles can be increased as the top of the car is prolonged.