Tumor necrosis factor-α (TNF-α) has been reported to inhibit adipocyte differentiation in which multiple transcription factors including CCAAT enhancer binding proteins (C/EBPs) and peroxisome proliferator-activated receptor (PPAR) γ play an important role. Induction of C/EBPα and PPARγ, which regulate the expression of many adipocyte-related genes, is dependent on the expression of C/EBPβ and C/EBPδ at the early phase of adipocyte differentiation. To elucidate the mechanism by which TNF-α inhibits adipocyte differentiation, we examined the effect of TNF-α on the expression of these transcription factors in mouse 3T3-L1 preadipocytes. TNF-α did not abrogate the induction of C/EBPβ and C/EBPδ in response to differentiation stimuli. In fully differentiated adipocytes, TNF-α rapidly induced C/EBPβ and C/EBPδ, whereas it downregulated the expression of C/EBPα and PPARγ. Our results suggest that TNF-α inhibits adipocyte differentiation independently of the downregulation of C/EBPβ and C/EBPδ.