The social organization of female mountain gazelles was studied on Mount Carmel, Israel. The behaviour of distinctly recognized individuals was studied by year-round observations. Female gazelles lived in groups whose composition remained constant throughout the year, and new females did not freely enter the established groups. Group home ranges overlapped, but various groups replaced each other in the same area at different times of the day. Different groups tended to use different parts of the overlapping home range. In general, but especially in summer, the different groups largely avoided being synchronously together in the same area. The occurrence of two groups in the same area at the same time was a rare event and when it occurred, a high rate of agonistic interaction was observed between the groups. Hence, groups of female mountain gazelles hold and defend temporal territories against other female groups. Mean seasonal group size ranged between 3.4 and 6.4 and was largest during winter, when groups of females joined together occasionally and little agonistic interaction was observed between the groups. It is suggested that group size is affected by food availability and predation pressure.