The static electric quadrupole interaction of 181Ta in HfOCl2∙8H2O and HfOCl2∙4H2O, incorporating the perturbed angular correlation of the 133–482 keV γ-rays cascade, has been measured. The quadrupole interaction frequencies obtained were ω1 = (1356 ± 65) mrad/s for HfOCl2∙8H2O, and ω1 = (858 ± 40) mrad/s, η = 0.58 ± 0.01 for HfOCl2∙4H2O. Comparison with other measurements is given.