A bicycle rear suspension system has a virtual pivot point that is close to a junction between a chain and a front driving sprocket when a piston rod travels relative to a cylinder body by ¼ to ⅓ of a maximum displacement value, and that moves rearwardly when a rear wheel moves upwardly away from the ground. A line interconnecting an instant center of a rear triangular frame and a contacting point between a rear wheel and the ground forms an angle of about 45° with respect to a horizontal line.