Objective:To examine the effects of tranexamic acid on epidermal melanocytes of mice after ultraviolet (UV) B ear irradiation.Methods:Twenty four female C57 mice, about 20 to 24 g on average, were randomly divided into normal saline group (NS), tranexamic acid group (TA), UVB/normal saline group (UVB/NS), and UVB/tranexamic acid group (UVB/TA). The UVB-irradiated group was locally irradiated to the ear with UVB at a dose of 250 mJ/cm 2 per day for 3 days. The UVB/TA group and TA group were orally administered tranexamic acid (750 mg/kg/d) at 30 min before UVB exposure; at the same time, the UVB/NS group and NS group were given to equal amount of normal saline by gavage. Cell counter and the morphological changes were accessed by using optical microscope in combination with Dopa staining. Quantitative real-time PCR (qRT-PCR) was used to detect the mRNA expression of tyrosinase (TYR), tyrosinase-related protein-1 (TYRP1), tyrosinase-related protein-2 (TYRP2) and microphtalmia transcription factor (MITF) of the ear. Results:According to the DOPA staining, there was no difference between the NS group and TA group. As compared with the NS group, the number of Dopa-positive melanocytes increased remarkably in the UVB/NS group ( t=6.653, P<0.01), the dendritics of these cells were numerous and prolonged ( t=6.364, 3.844, P<0.01). In comparison with the UVB/NS group, the expression of Dopa-positive melanocytes was significantly decreased in the UVB/TA group ( t=3.649, P<0.05), the number and length of dendrites were also alleviated with significant difference ( t=4.146, 2.197, P<0.05). The relative expression level of TYR, TYRP1, TYRP2, MITF in the skin of the ear was calculated via 2-△△CT method. The expression levels of target gene in the UVB/NS group were increased and had significant difference from that in NS group ( t=14.030, 5.427, 9.800, 5.891, P<0.05). While the mRNA expression levels of TYR, TYRP1, TYRP2 and MITF in the UVB/TA group were lower than those in the UVB/NS group, with statistically significant difference ( t=2.078, 1.905, 3.138, 1.732 P<0.05). Conclusions:Tranexamic acid suppresses UVB ear irradiation-induced epidermal melanocyte activation of mice by decreasing the mRNA expression levels of TYR, TYRP1, TYRP2 and MITF.