The objective of this study was to determine the effect of some environmental factors on the parameters and characteristics of the lactation curve in Iranian Buffalo ecotypes. The data consisted of 53222 test-day records in various stages of lactation and different parities recorded from 743 herds by Iranian Animal Breeding Center (ABC) during 1992-2005. The parameters and characteristics studied were milk production at the beginning of lactation (a); slope of the lactation curve up to the peak of milk production (b); slope after the peak of milk production(c); peak time; peak yield and persistency. Average milk yield, a, b, c, peak time; peak yield and persistency were 2340.8, 8.6, 0.6, 0.2, 3.2, 9.3, and 2.8 respectively. The effect of herd and year were significant on all parameters and characteristics of lactation curve (P<0.01). Season exerted a significant effect on milk yield, a, c, peak time and persistency (P<0.01). The effect of lactation period was significant on milk yield, a, c, peak yield (P<0.01) and b, persistency (P<0.05). Lactation period had no significant effect on peak time (P>0.05). Calving age had significant effects only on c, persistency (P<0.01) and b (P<0.05).