Aim To study the role of acylation stimulating protein for the differentiation of 3T3-F442A preadipocytes and explore the molecular mechanism of it. Methods There were two groups in this study: acylation stimulating protein (AsP) group(induced to differentiate by AsP) and control group(without inducers).The morphological changes were observed by Oil-Red O staining.Triglyceride(TG) synthesis and TG mass were assayed by chemical colorimetry. The cell were harvested on the 0~(th) day,1~(th) day,2~(th), 4~(th) day,6~(th) day after induced differentiation and total RNA of these cell were abstracted. The transcription factor peroxisome proliferator activated receptor γ(PPARγ), C/EBPα,C/EBPδ mRNAs expression were assayed by reverse transcription-polymerase chain reaction(RT-PCR). Results 3T3-F442A preadipocytes were induced to differentiate with AsP alone.Fat droplets were clearly visible in the cytoplasm of 3T3-F442A cell.The differentiation rate were high(80%) in AsP group. In AsP group TG synthesis and TG mass were significantly increased,both of them were higher than that of control group(p<0.05). PPARγ mRNA expression in the 3T3-F442A cell were low on 0~(th) day of induced differentiation,and it was increase significantly on the 1~(th) and 2~(th) day induced by AsP(p<0.05). It continued to increase significantly on the 4~(th) and 6~(th) day(p<0.05).The C/EBPδ mRNA were expressed in low level on 0~(th) day of differentiation induced by AsP and the expression level was increase significantly on the1~(th) and 2~(th) day of differentiation(p<0.05).But the expression of C/EBPδ mRNA was decreased on the 4~(th) and 6~(th) day,there were no significant difference compared with that of 0th day(p>0.05).The expression of C/EBPα mRNA was very low on the 0~(th) day of differentiation induced by AsP.It was increased on the 1~(th) and 2~(th)