Abstract: OBJECTIVE To explore the formulation composition of bimatoprost ophthalmic thermosensitive in situ gel by using the central composite design-response surface method and investigate its in vitro release. METHODS Poloxamer 407 and 188 were used as the gel matrix. The central composite design-response surface method was used to screen out the best prescription to obtain the appropriate gelation temperature. HPLC method was established to determine the content of bimatoprost and the release in vitro was investigated using a membrance-free dissolution model. RESULTS In the formulation, 1% tween 80 was used as the solubilizer, and the composition of 0.03% bimatoprost(w/v), 21% poloxamer 407(w/v) and 2% poloxamer 188(w/w) could reach the optimum gelation temperature. The results of in vitro release test indicated that the release of the formulation showed a linear relationship with time. CONCLUSION The in situ thermosensitive gel of pemirolast potassium prepared in this paper has good temperature sensitivity, which can prolong the residence time of the drug in the eye and is easy to administer. It is expected to be developed into a new ophthalmic dosing formulation.