Abstract: Objective:To investigate the influence of serum from patients with dermatomyositis/polymyositis(DM/PM) on the activity of human umbilical vein endothelial cells(HUVEC). Methods:The serum taken from 16 untreated DM/PM patients were enrolled in the DM/PM group who were evenly divided into pre-treatment group(8 cases) and post-treatment group(8 cases),and the serum from 13 healthy people acted as control. The HUVEC was cultured in vitro,and the influence of serum from patients with DM/PM on HUVEC was examined by MTT assay. Results:There was no significant difference in the activity of HUVEC between the DM/PM group and the control group(P>0.05). Compared with the control,the serum from the post-treatment group suppressed the proliferation of HUVEC at 24 h after treatment(P<0.01),but accelerated the proliferation of HUVEC at 72 h(P<0.05). Compared with the pre-treatment group,the serum from the post-treatment group suppressed the proliferation of HUVEC at 24 h after treatment (P<0.05),but no significant difference was observed between the two groups at 48 h and 72 h(P>0.05). Conclusions:The serum from patients with DM/PM may not affect or impair the activity of HUVEC in vitro; the serum from the post-treatment DM/PM patients may inhibit the activity of HUVEC after the first promotion in vitro.