The long non-coding RNAs (lncRNAs) are a type of RNAs with more than 200nt in length and without any long open reading frame, but often have mRNA structural features. They can regulate the expression of target genes in different manners at the transcriptional and post-transcriptional levels. In recent years, various studies demonstrated that lncRNAs play crucial roles in adipogenesis. The long non-coding RNA, lnc-RAP3, located on the mouse chromosome 17, possesses a significantly differential expression pattern during mouse adipocyte differentiation; but its specific biological function (s) remains unclear. To investigate the effect of lnc-RAP3 on adipogenesis in the mouse 3T3-L1 preadipocytes, we first constructed a eukaryotic expression vector pcDNA3.1-RAP3. pcDNA3.1-RAP3 and synthetic RAP3-siRNAs were transfected individually into 3T3-L1 preadipocytes by Lipofectamine TM 2000, thereby over-expressing and knocking-down lnc-RAP3 expression, respectively. The transfected preadipocytes were induced to undergo adipogenic differentiation. Oil Red O staining and qRT-PCR were used to detect the effects of lnc-RAP3 overexpression/knockdown on 3T3-L1 preadipocyte differentiation. The results showed that overexpression of lnc-RAP3 led to a notable decrease in lipid accumulation (P<0.05) and remarkably reduced the mRNA expression levels of C/EBPα, Glut4, PPARγ, LPL and FAS on day 0, day 2, and day 4 post differentiation (P<0.05, P<0.01). In contrast, quantitative analysis of Oil Red O on day 4 of differentiation revealed that inhibition of lnc-RAP3 increased the formation of neutral lipid droplets (P<0.05). In addition, silencing lnc-RAP3 also significantly increased the mRNA expression of PPARγ, LPL, C/EBPα, FAS and Glut4 on day 0 and day 2 post differentiation (P<0.05, P<0.01). Our study suggests that lnc-RAP3 might suppress 3T3-L1 preadipocyte differentiation by affecting the expression of the genes involved in adipogenic differentiation.