Objective: Our aims were to derivate horse ES cell lines by repeated passage of ICM cells and assess hLIF and bFGF effects on maintenance of their pluripotenciesMaterials and Methods: A basic medium was prepared for the culture of ICMs and horse embryonic stem cells using KODMEM supplemented with 10% FBS, 0.1mM Non-essential Amino Acids, 2mM L-glutamine, 1% Insulin-Transferrin-Selenium, 100mg/ml of streptomycin, 100 units/ml of penicillin and 0.1mM 2b- mercaptoethanol on γ-irradiated MEFs. ICM cells were recovered mechanically from day-7 blastocysts and cultured in basic medium on feeder cells. The culture medium was changed every day after first passage and the passage was performed by mechanical dissociation with a needle every 6-8 days until passage 15. The putative horse ESCs were cultured in the basic medium supplemented with human leukemia inhibitory factor (hLIF 40ng/ml) only, basic fibroblastic growth factor (bFGF 4ng/ml) only, or bFGF plus hLIF with MEF feeder cells. Colony morphology was evaluated, continuously. Finally, for determination of cell pluripotency, the hESCs were analyzed for markers of pluripotency. Immunostaning of the putative horse ESCs was done for Oct4, SSEA-1, GCTM-2, TRA1-60 and TRA1-81.Results: Derived ICMs, from day-7 blastocysts, were cultured with basic medium on MEF feeder cell monolayer. They grew as flat colonies including cells with different morphology (P0). Different morphological cells were transferred for next passages separately (P1). Cells in basic medium only, and basic medium added LIF could keep colony form similar to each other until passage 15. Although the cells in basic medium containing bFGF could produce some colonies in early passages, they could not maintain their morphology in later passages. Those colonies which were plated in basic medium added hLIF and bFGF did not grow after a few passages. After 15 passages, immunohistochemistry of the putative horse ESCs showed that some cells in the colonies were positive for Oct4, SSEA-1, GCTM-2, TRA1- 60 and TRA1-81. These results indicated that those cell colonies were not completely purified embryonic stem cells, but some of them were still pluripotent.Conclusion: Our study show the primary horse ESCs are able to self-renew when they are cultured in the basic medium on γ-irradiated MEFs. These results also indicated that cell colonies were not completely purified embryonic stem cells, but some of them were still pluripotent. ESC-like cell morphology of horse putative ESCs were well maintained in the basic medium supplemented with or without hLIF. This result suggests that hLIF is neither prerequisite nor negative for maintenance of horse ESCs; bFGF seem to be negative for maintenance of horse ECSs. The combination of LIF and bFGF is unable to improve the culture condition. Thus, the new factors need to be investigated further to maintain horse ESCs in purified population.