OBJECTIVES This study was designed to examine the embryotoxic potential of the curcumin at the blastocyst stage and during early post-implantation development of mouse embryos in vitro. STUDY DESIGN Curcumin was administered to ICR mice embryos at a dose of 0, 6, 12, 24 μM throughout in vitro culture. A total of 1015 embryos were randomly assigned to the different dosage groups. The embryotoxic effects were studied by the exposure of curcumin at the blastocyst, implanted blastocyst and early egg cylinder stages, respectively. For assessment of implantation in vitro and further embryonic differentiation, blastocysts were cultured for 8 days. The cell proliferation of outgrowth blastocysts was analysed by Giemsa staining. RESULTS Exposure to 24 μM of curcumin at the implanted blastocyst stage or early egg stage cause adverse effects on development. The percentage of embryos in the later stages of development was changed depending upon the dose of curcumin used. Furthermore, exposure to 24 μM of curcumin at the blastocyst stage was lethal to all embryos. The number of nuclei per outgrowth of the blastocyst decreased significantly after curcumin pre-treatment. The percentage of trophoblastic giant cells per outgrowth increased significantly after curcumin pre-treatment. CONCLUSIONS These findings demonstrate that curcumin exerts an adverse effect on mouse embryos during the early post-implantation stages of development, equivalent to day 3-day 8 of gestation in vivo. Curcumin treatment or administration should be used carefully at the early post-implantation stage of gestation.