Total of 1797 records of 765 cows raised in El-Shazly private farm . located in Shobratana – Basyon , Gharbia , Governorate were collected during period from 1985 to 1993 to study the effect of some environmental factors on milk production of Friesian Cattle . The result obtained could be summarized in the following . Parity had non- significant effect on all traits study except the effect on 90 days cumulative milk yield was highly significant (P< 0.01) .Year of calving and significant ( P< 0.01 ) effect on different studied traits . Season of calving had highly significant (P< 0.01) effect on cumulative 90 and 180 days milk yield, and only significant  (P< 0.01) effect on total milk yield , lactation period and on the five method used for estimating persistency of lactation .But it is had non significant effect on both 305 and 270 days milk yield .