Praseodymium dioxide (PrO2) -doped In0.69Ga0.31As0.67P0.33 layers are grown on semiinsulating In P substrates with liquid-phase epitaxy. The PrO2 doping of the growth solution varies from 0 to 0.32 wt %. The quaternary In0.69Ga0.31As0.67P0.33 layer composition determined with two-crystal X-ray diffraction and photoreflectance is found to be independent of the PrO2 concentration in the melt. The photoluminescence spectra measured at 12 K show both exciton and donor-acceptor peaks, the magnitudes of which depend on the PrO2 doping. The carrier concentration of the n-type quaternary layer decreases and the mobility increases with increasing PrO2 concentration and reaches the values of 8.3.1015 cm−3 and 7300 cm2/Vs, respectively, at about 0.1 wt% at 77 K. The experiments show that PrO2 has an impurity gettering effect in the growth process.