The results obtained using Z-Scan methods (transmission — TZ-Scan and multiple-pass — MZ-Scan) for the characterization of the partial transparent nonlinear optical materials (NOM) are presented. For a typical NOM, a monocrystalline Si wafer with thickness 0.4 mm, at % = 1060 nm, the nonlinear bulk effects are dominant in comparison with the nonlinear effects produced by the entrance interface (due to the sufficient large transmission of Si). In this case, the MZ-Scan at ow laser intensity (several MW/cm2) can be analyzed similarly to the TZ-Scan, considering the multiple passes inside the sample and linear Fresnel reflections on both sample faces. Due to these multiple passes inside the sample, the sensitivity of the method is increased. The nonlinear optical susceptibility experimentally determined by multiple-pass Z-Scan is in agreement with a theoretical estimation ofthis parameter, with the results of other treatments oF MZ-Scan and TZ-Scan and with its values obtained by two and four-wave mixing.