An angle adjuster for a bicycle seat that is disposed between a frame of a vehicle and a seat. The angle adjuster for a bicycle seat includes: a frame connector configured to be connected to the frame; a seat connector rotatably connected to the upper end of the frame connector and configured to support seat; an angle adjusting assembly including a main clutch fixing and releasing the frame connector and the seat connector, and controlling rotational angle of the seat connector with respect to the frame connector by the release operation of the main clutch; an operating lever configured to mount on the frame to operate the main clutch; and a wire connecting the main clutch with the operating lever and operating the main clutch, when the operating lever is operated.