This research was carried out to evaluate the influence of the year and calving season on the production, composition and mozzarella cheese yield index (PKM) of Murrah water buffalos. We analyzed a data set of 514 lactations collected from 2004 to 2008, recorded and archived in software of a farm located in Taipu, in the eastern region of Rio Grande do Norte State, Brazil. To assess the effects of calving season, the year was divided into a rainy season (from March to August) and a dry season (from September to February). Results showed that the year influenced daily production and PKM (P<0.05). However, no effects were observed on logarithm somatic cell count (LSCC), fat, protein and total dry extract (TDE). The season had no influence on the variables analyzed and no interaction was observed between the year and the season. The season and its interactions had no effect on water buffalo performance in relation to dairy production and PKM index of mozzarella efficiency.