Worldwide, the loss and fragmentation of natural habitats, especially tropical forests, lead to a multiplication of contacts and conflicts between humans and wild primates. Developing means of population control and strategies for coexistence is urgently needed. Surprisingly, while birth control programs are spreading, particularly in Asia, the assessment of their efficiency and impacts on primates’ behaviour remains a neglected area of research. The main goal of this research is to test the effects of birth control programs on social dynamics of wild primate populations living in urban environments. We take advantage of an ongoing female sterilization program in one population of long-tailed macaques (Macaca fascicularis) living in a sanctuary in Bali (Indonesia) to address research questions concerning the impact on individual and social behaviour. This research aims to measure the implications of birth control on sexual competition and social network. We present here preliminary results in Ubud of the 6 first months after the first sterilization event of July 2017. These preliminary results showed that the first sterilization campaign does not seem impacting on stress levels, infant interest-related behaviours or centrality of the sterilized females (distances: contact, <1m, <5m). Even if there are not significant results, the sexual motivation of these females is preserved and shows a slight increase. The mean time that the sterilized females are inspected is longer than for the control ones, probably because the former are longer available for mating. The inter-birth intervals are around 1 year for this species, so we will keep going working on our dataset to study on a long-term basis the potential behavioural changes due to the sterilization program.