Abstract: Abstract Object:To investigate the effect of intradermal microinjection of Tranexamic Acid on Melasma’s melanocytes and melanin, to provide experimental evidence for treating Melasma. Methods: To establish Melasma Models with Guinea pig by UVB. Then, these models were divided into experimental group and control group. The pigmental spot of experimental group were intradermal microinjected with Tranexamic Acid. The change of number of melanocytes and melanin granules in both groups were observed in the immunohistology and Masson Fontanna-Ponceau staining.Result: The change of melanocyte in Melasma pigmental spot which microinjected with Tranexamic Acid, was not significant compared with before injection（P>0.05）. But the contents of melanin was obvious decrease（P<0.05）.Conclusion:There are inhibitory effect of Tranexamic Acid on the melanin granules,but no effec on melanocytes.

Key words: melanocytes, Ultraviolet