Abstract: To understand the endangered mechanism of the rare and endangered plant Handeliodendron bodinieri，flowering biology and breeding system were studied by using field investigation，out-crossing index estimation，pollination characteristics analysis and artificial pollination experiments. The main results were as follows：（1）H. bodinieri bloomed once a year and blooming time lasted from late April tomid-to-late May. The starting date of flowering or withering and the duration of blooming time was greatly influenced by local climate.（2）Most flowers of H. bodinieri were pseudo-bisexual flowers，which meant they were morphologyical bisexual flower with pistil and stamen，but functional unisexual flower that either pistil or stamen selective abortion during sex determination. It was rarely observed bisexual flowers with fertile pistil and stamen. Pseudo-bisexual flowers and bisexual flowers appeared on different trees. The unisexual flowers usually were dioecious. The number of female trees was smaller than that of male trees. The length of inflorescences in female tree was 5.6cm shorter than that of male trees. The duration of blooming time in female tree was 2 weeks shorter than that of male trees. It was occasionally observed female flowers on male trees.（3）The flowering process followed five stages from flower buds sprouting，white appearing，petal spreading，fully blooming to flowers withering，which took 5–6 days. The viability of pollen in male flowers was 90.5% from sprouting to 1 day after blooming，however，it descended greatly after 2 days of blooming. Some of stigmas of the female flowers were receptivity before opening while all stigmas were receptive for 1–3 days after petal fully opened. So the life span of pollen viability and stigmas receptivity were overlapped.（4）Each male flower had 51 461 pollens and each female flower had 6 ovules. The ratio of pollen to ovule（P/O）was 8 577，and the outcrossing index was 4. Taking all the results together of artificial pollination，bagged，netted and free pollination experiments，it indicates that H. bodinieri breeding system belongs to obligate outcrossing，apomixes may exist and pollinators are necessary for the pollination process.（5）Sex determination of flowers in H. bodinieri was complicated. The major factors leading to the endangered status of H. bodinieri in reproduction may include the limited fertile flowers and the large spatial isolation of female and male flowers as well as the unstable pollination environment.

Key words: Handeliodendron bodinieri, flowering biology, breeding system, floral sexuality