To study the effects of environmental factors on milk and fat yields (240day) traits of Iranian buffaloes, 22596 and 22165 records were utilized for milk and fat yield traits, respectively. Uni and bivariate analysis for estimation of (co)variation components of the traits were done in five lactations. Milk yield in the 1st lactation had the highest number of records (4482), collected through Center of Animal Breeding during 1986 2009. Estimation of genetic trends for both traits in the 1st lactation was also done. All factors except age at calving and season of calving exerted significant effects (p<0.01) on mile yield. Also all factors except age at calving significantly affected fat yield (p<0.01). High additive genetic variation was observed in this population and resulted in high heritability for either of the traits. Average heritability obtained from single and double trait genetic analyses for milk yield at five lactations were 0.49, 0.41, 0.54, 0.47 and 0.35 while for fat yield they amounted to 0.45, 0.36, 0.55, 0.40 and 0.50, respectively. Genetic correlations of milk yield in different lactations were higher than those for fat yield in different lactations. Genetic correlations among milk and fat yields in different lactations were high and positive.