A cordless roller shade includes a head unit (1), a shading face (2) mounted on the head unit, an elastic dynamic device (13) mounted on the head unit, and a bottom unit (3) mounted on the shading face. The elastic dynamic device includes a spring (133) having a thickness ranged between 0.1 mm and 0.2 mm. The bottom unit includes at least one balance member (33) having a determined weight ranged between 0.1 kg and 1.2 kg, and the shading face and the bottom unit have a total weight ranged between 1 kg and 5 kg, to balance the torque of the spring of the elastic dynamic device, so that the shading face is moved by the bottom unit to a determined position and is located at the determined position.