A study on blossom biology of jackfruit was carried out during February, 2000 to May, 2001 at Jackfruit Research Project, Bangladesh Agricultural University, Mymensingh. Eight germplasm (Nos-14, 16, 25, 29, 20, 45, 46 and 58) of same age were selected for the study. The period for the floral bud development varied from 51 to 75 days with an average of 59.4 days. Six different sequences of spike opening was observed on footstalk. The availability of pollen grains and receptivity of female spikes ranged from 4 to 7 days (ay. 5.3 days) and 19 to 32 days (ay. 26 days), respectively. The peak emergence of anther and its dehiscence occurred during 2-4 P.M. and 4-6 P.M., respectively and the peak emergence of stigma at 8-10 A.M.