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We report the synthesis and the magnetic susceptibility of (pipdH) 2 Cu 1-x Zn x Br 4 (pipd=piperidinium), which is a nonmagnetic impurity-doped S=1/2 spin ladder system. The samples were synthesized from a solution by using a slow evaporation method. Samples were confirmed to be in a single phase and to have the same crystal structure as the pure system (pipdH) 2 CuBr 4 by using X-ray diffraction measurements. To check the magnetic properties, we performed magnetic susceptibility and magnetization measurements with a superconducting quantum interference device (SQUID) magnetometer. A plot of the inverse magnetic susceptibility indicates the presence of dominant antiferromagnetic coupling. The magnetic susceptibility shows a broad maximum due to low dimensionality and a spin gap behavior related to the two-leg spin ladder at low temperature. The spin gap and the Curie constants of Zn-doped samples, as estimated from an analysis of the magnetic susceptibility, monotonically decrease as the Zn concentration decreases. A nonmagnetic impurity of S=1/2 spin ladder system affects the spin gap. : 75.30.Cr, 75.10.Kt PACS numbers