During the past decades, optical Kerr gating (OKG) evolved to one of the most important optical switching techniques for broadband analysis of ultrafast optical processes [1]. For maximum OKG efficiency a perfect overlap of the pump and probe fields is crucial for the whole propagation through the Kerr medium. Generally however, this overlap may not be optimal for the entire propagation due to a dispersion related walk-off between the pump and probe pulses. In this work the influence of this walk-off on OKG is investigated as a function of the material dispersion and the spectral separation between the pump and probe pulses: A linearly polarized white light continuum (probe), generated by focusing a sub-100fs pulse (central wavelength of 530 nm) into a 2 mm thick z-cut quartz crystal is superposed with a strong 60fs pump pulse (central wavelength of 800 nm, linear polarization tilted 45 degrees versus probe polarization) inside a variety of transparent media (fused silica, SiO2-Al2O3-La2O3 glass, Schott SF56, tellurite glasses and nanocrystalline (nc) ZnS), feasible for OKG. The transmitted probe signal is measured polarization selectively as a function of the delay between the pump and probe pulses by a spectrometer (Ocean optics USB4000). Fig. 1 displays the temporally and spectrally resolved Kerr signals obtained by a 0.6 mm thick sample of fused silica (left) and a 1.17 mm thick nc-ZnS sample. The n2 value of the ZnS is much larger than that of SiO2 [2, 3] and hence ZnS should be much more suitable for efficient OKG. The gating time of ZnS, however, increases from about 150 fs to more than 1 ps with increasing spectral separation between the pump and the probe fields, whereas that of fused silica stays below 100 fs over the whole spectral range. Group velocity mismatch between the pump and the probe fields, leading to a temporal walk-off is considered to be the major reason for the observed pulse lengthening in the high refractive index material. Furthermore a finite interaction length between pump and probe will limit the OKG efficiency. In order to prove this assumption, the temporal walk-off is simulated by a simple propagation model with its simulation results being in good agreement with the experiment findings.