Abstract: Pollination biology of Acacia mangium Willd. was investigated at aspects of floral phenology, floral morphology, anthesis, pollination success and so on through routine observation combined with optical microscopy and scanning electron microscopy (SEM) in clone seed orchard at Shazui Town, Jiangmen City, Guangdong Province. The result showed that the A. mangium flowers between Sep. and Oct. Its flowering was not continuous, containing 6 to 7 flowering stages. Individual plant flowered in synchrony, showing the "mass-flowering pattern". The spike inflorescence consists of (172.7±27.1) flowers, including hermaphrodite flowers and male flowers. The male flowers account to (10.35±7.78)% per spike. The pistil contained (14.11±1.05) ovules with a long, solid style. Cup-liked stigma was suitable for one polyad, which comprising 16 pollen grains. The pollen to ovule (P/O') valued 1.13. When anthesis began, Pistil was the first organ to extend and receptive making protogynous sensible. SEM revealed that the dehiscent lines existed at Stage2 and 3; however, the anthers began to dehisce at Stage 4, about 7:00－9:00 following abundant pollen shedding at 9:00－12:00. The stigmas gone through morphology changes showed as exudates were emerged apparently during the first half-day after anthesis, predicting the coming of receptivity period. The results will helpful for Acacia breeding in the future.