The objective of this study was to evaluate the effect of some factors on somatic cell count (SCC) in milk, milk yield (MY) and milk compassion, as well as he relationship between SCC, MY and milk quality of Friesian cows. A total of 1250 test-day were studied for 145 dairy Friesian cows during the consecutive period from March 2009 toApril 2010 were collected. All Friesian cows ranged between 400 and 600 kg live body weight, 3 -13 years of age and 1- 8 parities. Cows of the experimental period were fed concentrate feed mixture (CFM), berseem hay, rice straw and corn silage (summer ration) and CFM, fresh berseem and rice straw (winter ration). Throughout the experimental period, cows were machine milked and daily milk yield was individually recorded. Milk composition was determined. Milk samples for SCC determination were collected monthly of calving to the end of lactation. Results revealed that SCC significantly (P<0.05) decreased in second and third- parities and higher in four and fifth parities. Milk yield was significantly (P<0.05) higher in second parity, and decreased in other parities. The SCC was significantly higher in summer, moderate in spring and lower in winter and autumn seasons. Milk yield was significantly higher in winter, moderate in autumn and decreased in summer and spring seasons. Milk protein and lactose were significantly higher (P<0.01) in summer and lower in winter season. The SCC, milk protein and lactose increased in summer ration, but MY decreased significantly (P<0.05) in summer ration. Somatic cell count increased significantly (P<0.01) at first 30 days of lactation (469×103 /ml) (early lactation), highly significantly (P<0.001) in the end of lactation (597×103 /ml), and deceased after 90 and 180 days of lactation. Milk yield was significantly (P<0.05) decreasedby increasing SCC. Protein content was significantly (P<0.05) larger in milk (2.42 to 2.81), when SCC increased (200×103 )to 1000×103 cell/ml milk. An Increase in SCC during the late of lactation was accompanied with decrease in MY, fat, lactose percentages and milk quality.