Astragalus argaeus is an endemic plant species that is under critical risk of extinction. Here we investigated its population census, breeding system and reproductive success to determine the main factors affecting restricted distribution of this species. According to the results from pollination experiments, A. argaeus was autogamous but benefit from the cross pollination (xenogamous) and the presence of pollinators increases fruit set. The pollen/ovule ratio of A. argaeus was calculated as 3119,which correspond to facultative xenogamy. Reproduction biology data obtained by both methods are quite compatible with each other. Pollen viability and stigma receptivity data showed that both stigma receptivity and pollen viability were high and was no temporal isolation throughout the anthesis. Seed viability of A. argaues was determined as 52%. The low reproductive success of the species could be attributed to low seed viability and germination rates, small population size and variations in season and climate.