Records of somatic cell score (SCS) and 305 day milk yield (MY) of the Friesian cows raised at Sakha and El-Karada farms. From 2000 to 2017 were used to determine the relationships between SCS and MY between and within first five lactations. Genetic parameters were estimated by MTDFREML. Heritability estimates of SCS was ranged from 0.11 to 0.23 for five first lactations and were from 0.21 to 0.36 for MY. Heritability estimates for all lactations were 0.30 and 0.41 for SCS and MY, respectively. The genetic correlations between (SCS and MY) were moderate to high and positive (0.60 to 0.81) for first five lactations. Additionally, genetic correlations between (SCS and MY) were increased with increased lactation order, indicating a selection for MY will reduce SCS and therefore reduce the incidence of mastitis. Accuracy of (EBV's) varying from 64 to 84, 42 to 78 and 30 to 53% of sires, cows and dams, successively, indicating, the genetically improvement could be achieved with any pathway of them. Also, the trend of correlations between predicted breeding values were in the same direction with those reported for genetic correlations for the same traits. Selection of the cow on the basis of their expected breeding values should cause reduction in the SCS and therefore reduce incidence mastitis and increase MY. The accuracy of the selection index that included SCS with MY was higher than that of other indices. It is emergent to include SCS as a criterion for selection of mastitis resistance in the breeding programme in Friesian cows.