Information about reproductive systems of pasture plant species help to determine their genetic variation potential and adaptability, when planted in a new condition. Due to the importance of Onobrychis as a fodder plant, pollination mechanisms of thirteen Onobrychis populations of annual species O. crista-galli, O. pulchella, O. caput-galli and O. micrantha together with O. viciaefolia and O. altissima as perennial species were examined based on morphological characteristics of flower, pollen/ovule ratio and quantity of fruit and seed production in natural and isolated pollinations. The results showed that flower length in O. viciaefolia and O. altissima was longer than that in other species. Style length was also longer than filament length in these two species. The most pollen/ovule ratio belonged to O. viciaefolia (22211) and the least belonged to O. crista-galli 387 (2) (840). Seed and Fruit production in all species in tripping and isolated methods were similar to those in natural pollination, but in completely isolated condition seed and fruit were not produced in the perennial species. Based on the sum of the results it can be concluded that the perennial species O. viciaefolia and O. altissima are obligate xenogamy and the annual species O. crista-galli, O. pulchella, O. caput-galli and O. micrantha are facultative.