Abstract:Through the observation of the flowering sequences and gender of the inflorescence of Jatropha curcas L., the result shows that gender of apical flower has close correlation to flowering time, and also with the gender of other flowers on the same inflorescence. If the apical flower opened on the first day, the possibility of being female flowers is only 23.2%. But if the apical flower opened after the second day, the possibility would be over 85%. Meanwhile, if the apical flower was female, the possibility of inflorescences having other female flowers is 80%. But if the apical flower was male, the inflorescence will have no more female flowers. Understanding of flowering behavior and sex determination mechanism of Jatropha curcus is vital for manigulating gender expression, productivity improving, and breeding of new high productivity variety.