Optical Kerr lens spectroscopy has been employed to study the reorientation dynamics of N 2 O and CO 2 at the reduced densities 0.8–2.0 and different temperatures in a newly constructed high pressure cell. The transient birefringence induced in the medium by an ultrashort (110fs) non-resonant pump beam at 400nm was monitored by a second, time-delayed non-resonant probe beam at 800nm. The transient change of the probe beam diameter was detected in the far field using a small-area photodiode. Measurements employing parallel and perpendicular polarization allowed us to extract the nuclear and electronic components of the Kerr effect, where the latter one was by far weaker for both CO 2 and N 2 O. Accurate time constants for the reorientation dynamics of the CO 2 and N 2 O molecules were extracted from the tail of the nuclear Kerr response. In the case of CO 2 the time constants τ reorientation were between 210 and 280fs and in good agreement with previous data from NMR and OHD-OKE experiments as well as MD simulations. Reorientation time constants for N 2 O were in the range between 200 and 340fs, and thus very similar to CO 2 . In the density range studied, τ reorientation increases with increasing viscosity and decreasing temperature, in agreement with Stokes–Einstein–Debye diffusive models.