A total of 3748 normal lactation records of Friesian cows kept at Sakha farm, belonging to Animal Production Research Institute, Ministry of Agriculture, Dokki, Cairo, Egypt during the period from 2000 to 2006 were used in the present study. Data was analyzed by using Multiple Traits Derivative Free Restricted Maximum Likelihood (MTDFREML) according to Boldman et al. (1995) using repeatability animal model.  Two models were used. Model 1 includes month and year of calving and parity as fixed effects and direct genetic, maternal genetic, covariance between direct and maternal genetic and residual as random effects. Model 2 is similar to Model1, while additive maternal and covariance between direct and maternal effects were omitted from the model. Estimates of heritability for 305 day milk yield, lactation period, fat % and protein % were 0.33, 0.02, 0.16 and 0.64, respectively for model 1, while the values were 0.34, 0.03, 0.17 and 0.65, respectively as estimated from model 2. The removal of additive maternal genetic effects and covariance between direct and maternal genetic effects from the model increased estimates for heritability of additive genetic effects by 0.01, for the four traits. Therefore, the additive maternal genetic effect and covariance between direct and maternal genetic effects do not seem to make important contributions to the phenotypic variance for milk yield and it's composition.