Sapium sebiferum seeds were harvested from the marked donor individual at five developmental stages of maturity to study the changes in fresh weight, dry weight, moisture content, germination percentage, endogenous inhibitor activity, and plant growth regulators (PGRs) content. Moisture content of seeds declined from 46.98% (collected on September 1) to 12.00% (collected on November 1). Fresh weight decreased while dry weight increased significantly during seed development. Germination inhibitor activity in the seed coat and endosperm increased during seed maturation and at the same developmental stage, and inhibitor activity in the seed coat was higher than that in the endosperm. Excised embryos were capable of germinating for seeds collected on September 16, and maximum germination percentage was observed for seeds collected on October 16. With increasing seed maturation, gibberellins (GAs) content decreased while abscisic acid (ABA) content increased in both the stratified and untreated seeds. Compared to the untreated controls, the stratified seeds were consistently found to have lower ABA content and higher GAs content throughout different developmental stages. During the course of seed development, the GAs : ABA ratio was found to steadily decrease in both the stratified and untreated seeds, with an exceptional observation for seeds collected on October 1 that underwent stratification. With increasing seed maturity, the germination of untreated seeds initially increased but declined after October 1. Stratified seeds showed the same trend, with higher germination percentage than the control at all developmental stages. Results of this study showed that seeds harvested in September were immature and incapable of germinating, whereas those harvested in November were fully mature but showed strong dormancy. This study showed that seeds are ready to harvest on October 1, and they will be naturally dispersed in November. Thus we propose to harvest seeds before the middle of October for rapid and efficient germination.