[en] The effect of Sn-doping in (Pb,Cu)Sr₂(Y_0.6Ca_0.4)Cu₂O_z was investigated. The results of the X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-AES) and energy-dispersive X-ray (EDX) on Scanning Electron Microscope (SEM) analysis showed that the obtained material contained the phase 1212. The EDX analysis in different points showed that Tin was present in most of the microcrystals but its distribution was inhomogeneous. The resistivity and susceptibility measurements denoted superconductivity at T_c = 20 K. The dependence of the resistance on the magnetic field showed about 20 % of magnetoresistance effect at 4.2 K. The low values of T_c and the magnetoresistance were explained by assuming that a part of Sn occupied Cooper positions in the CuO₂ planes. (authors)