Abstract: Bidens pilosa is one of the noxious invasive weed in Asteraceae. We studied reproductive traits of this species such as phenology of capitulum, ratio of pollen to ovule (P/O), self-compatibility, pollen viability, visiting insects and germination potential of seed (achene) by experimental observation and bagging treatment in order to assess the association of these reproductive traits with invasiveness. B. pilosa flowered during October to November . The lifespan of a single capitulum was approximately 5 to 6 days. The cylindraceous nectary encircled the stylar base of each floret. Bagged capitulum showed high seed set potential which means self-compatibility and high pollen viability during flowering. The P/O ratio was 1 754.12±29.87, which suggests that the breeding system was facultative xenogamy. The main floral visitors were insects of Lycaenidae, Pieridae and Braconidae. Our results associated with those of others show that the reproductive traits of a versatile mating system of self- and cross-pollination in B. pilosa are important factors attributing to invasion of this weed. Moreover, other traits, such as the high production of achenes (seeds ), high germination percentage and rapid germination rate, as well as high dispersal capability of achenes, might contribute to the species’ successful invasive capability too.