In this paper, a new idea is proposed in order to modify the conventional Wilkinson power dividers for size reduction. The proposed structures contain Step Impedance Transmission Lines (SITLs) instead of the uniform ones, with reduced length at the design frequency. The impedance ratio of SITLs is considered variable and written as the total electrical length of the lines. With this additional design parameter and a higher degree of design freedom, the size of the dividers is reduced. One Wilkinson divider is designed and fabricated for operation at 1.00 GHz. The proposed Wilkinson power divider has a size reduction more than 55%. The measured results of the fabricated power dividers are in good agreement with the theoretical ones.