Aim To explore the effect of niacin on cholesterol efflux in fully differentiated 3T3-L1 cells and the possible mechanism.Methods Fully differentiated 3T3-L1 cells were incubated in the medium containing various concentration of niacin(0～1.0 mmol/L) for 24 h(n=6).Reverse transcription polymerase chain reaction(RT-PCR) was used to evaluate adipocytes mRNA expression.Cholesterol efflux rate was determined through measuring release of radioactivity from 3H-cholesterol prelabled cells into medium containing apolipoprotein A_Ⅰ.Results Niacin could dose-dependently increase adenosine triphosphate binding cassette transporter A1(ABCA1) mRNA expression and apolipoprotein A_Ⅰ-mediated cholesterol efflux in 3T3-L1 cells,but had no effect on scavenger receptor class B type Ⅰ mRNA expression.Peroxisome proliferator-activated receptor gamma(PPARγ) presented high level expression in fully differentiated 3T3-L1 cells.Compared with control(0.38±0.29),niacin significantly enhanced PPARγ mRNA expression.The maximal induction was obtained with 1.0 mmol/L of niacin.Conclusion Niacin could enhance the ABCA1 pathway in adipocytes,up-regulate PPARγ mRNA expression,then increase cholesterol efflux.This new action of niacin might provide rational explaination to the mechanisms of raising high-density lipoprotein cholesterol.