A bicycle brake system includes a first arm unit having a first arm and an engaging slot. A second arm unit is located in the engaging slot and has a second arm. The first and second arms each have a brake pad and the two brake pads face the two sides of the wheel rim. A cam unit has a contact piece connected to the second arm unit and a cam member pivotably connected to the first arm unit. The cam member includes a cam portion having a curved surface which is in contact with the contact piece. An operation unit is connected to the second arm unit and includes a cable which is fixed to the guide portion of the cam member. The cam member indirectly contacts the second arm unit so that the second arm unit does not wear out.