The low temperature heat capacity measurements on LSCO samples containing Zn impurities have been performed by means of pulsed differential calorimetry technique. The interpretation of the Zn- concentration dependence of the residual g-coefficient in the linear temperature part of Cel(T) at T<<Tc is consistent with a model based on the assumption of the d-wave symmetry of the order parameter of these superconducting copper oxides.