In this work, the growth and activity of natural kefir starter and kefir grains starter cultures were evaluated in fermented cow and buffalo kefir. Viable cell counts of natural kefir starter and kefir grains starter cultures, physicochemical properties, viscosity, concentration of ethanol and sensory evaluation of the kefir samples were determined during refrigerated storage at 5±1°C for 21 days. Kefir made from buffalo milk by kefir grains cultures (KG-B) showed better retention of viability, ethanol content, viscosity and decreased the sensory properties comparing with another samples. The best sensory properties were noticed in kefir made from cow milk by natural kefir (KS-C), then after kefir made from cow milk by kefir grains (KG-C) respectively. Thus, the study demonstrates that the kefir production from cow milk using natural kefir starter culture may be preferred under Egyptian conditions which had the lowest ethanol concentration and will be accepted by Egyptian consumer.