Ormosia calavensis has long been exploited as a conventional medicine for various illnesses. This study aimed to evaluate the cytotoxic activity of the ethanolic leaf extract and fractions of O. calavensis against sea urchin embryos. Results showed that O. calavensis ethanolic extract demonstrated antimitotic activity with IC50 values of 20.47 µg/ml, 9.22 µg/ml and 0.73 µg/ml in the first and third cleavage and blastula, respectively. Furthermore, all fractions of O. calavensis exposed to sea urchin embryos exhibited significant antimitotic activity across the three stages of embryo development. Moreover, the ethyl acetate fraction of O. calavensis had the lowest IC50 values of all the tested samples in the first and third cleavage and blastula, with IC50 values of 20.85 µg/ml, 7.02 µg/ml and 3.53 µg/ml, respectively. The IC50 values for mitotic activity inhibition decreased in the succeeding stages of embryo development in the said plant. This suggests that mitotic activity was inhibited in the subsequent phases of sea urchin development. Moreover, the various test plant fractions exhibited concentration rising dependent effect, as the antimitotic activity increased in relation to the concentrations of the fractions. The concentration dependent increase in bioactivity observed in O. calavensis indicates the presence of cytotoxic compounds in the plant.