The authors not only observed flowering phenology, flowering pattern, species of visiting insects, visitation rate of pollinators and their foraging behavior, but also studied pollen viability, stigma receptivity, pollen-ovule ratio, effect of insect pollination and breeding system. The results indicated that Eleutherococcus brachypus was in the progress of vegetative propagation and a population was a clone. A given flower kept open for about two days, but successive bloom of the flowers in a population lengthened its florescence for about 20 days. The pollen-ovule ratio (P/O) was about 2500～3200. On the first day when Eleutherococcus brachypus was in bloom, the pollen grains shed. The viability of polen was over 90% and it lasted for over five days. The stigma has a receptivity of 10 days or so. Nectar secretion started on the first day and continued for about 10 days. Although it was physiologically self-compatible, pollinator visitation could highly enhance fruit set. The invectors chiefly visited between 1200 and 1400 hours. Insects pollinated mainly among different flowers of the same clone, which, in a broad sense, belonged to self-pollination. Pollinators were diverse small insects such as smallbees, wasps, flies and beetles. Artificial pollination experiments showed that under natural condition, the number of pollen on the stigma was inadequate. [WTBX]Eleutherococcus brachypus adapted to the habitat by such characteristics as its flowering season, high pollen viability, long time stigma receptivity and nectar secretion duration, thus its higher fruit set produced. The average fruit set ratio of Eleutherococcus brachypus was 65% while plump seed ratio was 45.5%. No seedling was found in the field. It seems that the poor quality of seeds caused by inbreeding depression accounted for this. The poor quality of seeds also limited the distribution of Eleutherococcus brachypus.