Abstract: Yao Qiunan,Wei Zhiping, Liu Yanqun Department of Dermatology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou 221002, Jiangsu, China （The current affiliation of the third author was Jiangsu Medical Association） Corresponding author: Wei Zhiping, Email: xzwzp1961@aliyun.com 【Abstract】 Objective To evaluate effects of cucurbitacin I on in vitro proliferation of HaCaT cells and the of keratin 17 （K17）, signal transducer and activator of transcription 3 （STAT3） and vascular endothelial growth factor （VEGF） in cultured HaCaT cells. Methods In vitro cultured HaCaT cells were divided into 6 groups to be treated with cucurbitacin I at different concentrations of 0.0125, 0.025, 0.05 and 0.1 μmol/L （0.0125, 0.025, 0.05 and 0.1 μmol/L cucurbitacin I groups）, DMEM containing the same volume of DMSO as 0.1 μmol/L cucurbitacin I （DMSO group）, DMEM （negative control group） and 10 nmol/L calcipotriol （positive control group）, respectively. Cell counting kit?8 （CCK8） assay was performed to assess in vitro cellular proliferative activity after 12?, 24?, 36?hour treatment, reverse transcription （RT）?PCR to measure the mRNA of K17 and VEGF in HaCaT cells after 24?hour treatment, and Western blot analysis to determine the protein of K17, STAT3, phosphorylated?STAT3 （p?STAT3） and VEGF after 24?hour treatment. Statistical analysis was carried out by one?way analysis of variance （ANOVA）, repeated measures ANOVA, Student?Newman?Keuls （SNK）?q test and Pearson correlation analysis. Results The proliferative activity of HaCaT cells started to decrease after 12?hour treatment with cucurbitacin I at the concentration of 0.0125 μmol/L. When the concentration of cucurbitacin I increased up to 0.1 μmol/L, the cell proliferation rates were inhibited by 43.00% ± 2.11% and 48.98% ± 2.27% after 24? and 36?hour treatment respectively. Compared with the negative control group, cucurbitacin I at different concentrations all could inhibit in vitro proliferation of HaCaT cells （all P < 0.05）, and the inhibitory effects increased gradually with the increase of cucurbitacin I concentration and treatment duration. After 24?hour treatment, the mRNA of K17 and VEGF and the protein of K17, VEGF and P?STAT3 were significantly decreased along with the increase of concentration of cucurbitacin I （all P < 0.05）. Conclusion Cucurbitacin I can inhibit in vitro proliferation of HaCaT cells, and down?regulate the mRNA of K17 and VEGF and protein of K17, VEGF and P?STAT3.