Objective To investigate the effects of microRNA-29a (miR-29a) on lipopolysaccharide (LPS)-induced apoptosis in human monocytes THP-1 cells in order to understand the molecular mechanisms.Methods Human monocytes THP-1 cell line were exposed to LPS after transfected with miR-29a inhibitors (100 nmol/L) or just transfected with miR-29a mimic (100 nmol/L) by lipofectamine RNAiMAX.Flow cytometry (FCM) was used to detect the cell apoptosis.Real-time RT-PCR was employed to measure expressive levels of the gene Bcl-2 and Mcl-1.The luciferase assay was performed in HEK293T cells,which were co-transfected with plasmid DNA and miRNA by using Lipofectamine 2000.Statistical analysis carried out by using SPSS 13.0 software for One-way ANOVA and Student' s t test.Results Transfection with miR-29a mimics for 48 h increased apoptosis rate and significantly reduced the expressions of Bcl-2 and Mcl-1 in THP-1 cells in comparsion with the control group.The apoptosis rate also raised in THP-1 cell stimulated by LPS for 24 h followed by LPS stimulation for 24 h,the apoptosis rate was decreased in comparison with the LPS group.In addition,our luciferase assay data showed that HEK293T cells cotransfected with miR-29a mimics and Bcl-2 3 ' UTR-Wt or Mcl-1 3' UTR-Wt plasmid significantly reduced the luciferase activity compared with the control group.Conclusions The miR-29a may regulate apoptosis by targeting the genes Bcl-2 and Mcl-1,and miR-29a may play a pivotal role in the process of apoptosis in immune cells.