Abstract: ObjectiveDevelopmental law of oil palm female and male inflorescences were studied, and the differ-ences between pistillate flowers and staminate flowers in morphology and cytohistology were investigated, in order to lay foundation for further sex differentiation research. MethodThe inflorescences were collected at different developmental stages, their length and mass were measured. Then, the paraffin sections were made, so as to observe its cytohistology characters with microscope. ResultThe whole developmental process of oil palm inflorescences could be divided into two stages viz., sex unrevealed stage and sex revealed stage. The development at sex unrevealed stage took more time than that at sex revealed stage, accounting for 80% of total period. There was a exponential growth stage to be found between sex unrevealed stage and sex revealed stage, at this stage, both length and mass of inflorescences increased rapidly and expo-nentially, it was denominated exponential growth stage of inflorescence(EGSI). At beginning of floral sex differentiation, the oil palm inflorescences started to develop rapidly, entering EGSI. The remarkable differences between pistillate flowers and staminate flowers during developmental process were as follows: There was a bisexual period during developmental process of pistillate flower, and pistillate flower was composed of a single pistillate flower flanked by two accompanying staminate flowers, then accompanying staminate flowers selectively aborted and the pistillate flower transformed into an u-nisexual flower; however, there was not a bisexual period during developmental process of a staminate flower, and stami-nate flower directly entered unisexual stage after sex differentiation. Moreover, there were some significant differences in number of floral primodium meristem between male and female inflorescences, and that of male inflorescences was more than that of female, with some differences in order of magnitude. ConclusionThere exist EGSI during developmental process of oil palm inflorescence. And there are some significant differences in number of floral primodium meristem be-tween male and female inflorescences. According to numbers of floral primodium meristem, the gender of a young inflores-cence which has not emerged from the base of the relevant leaf can be judged.