Total of 893 lactation records collected during the period (1983-1993) on a herd of 281 buffaloes and 21 sires raised at Mehallet Mousa, Station, Animal Production Research Institute, Ministry of Agriculture, Egypt, were used to study some genetic and non-genetic factors affecting monthly and cumulative monthly milk yield. Effects of sire, generation number, year of calving and parity  were highly significant for most of the traits studied except season of calving which was not significant. Heritability estimates of all traits were low and positive, they ranged between 0.06 to 0.19. Estimates of genetic correlation between each of monthly milk yield at the 3 rd and the 4 th month and cumulative monthly milk yield at 90 and 120 days and 300 days milk yield were positive and high about 1.02-1.09. Also, phenotypic and environmental correlation between the traits studied and 300 days milk yield were positive and either moderate or high, ranging between 0.35 and 0.99.