Although tumor necrosis factor α (TNFα) decreases the expression of peroxisome proliferator-activated receptor γ (PPARγ), its mechanism is not understood. We evaluated the effect of ceramide, the second messenger of TNFα, on the expression of PPARγ in primary cultured adipocytes. PPARγ mRNA and aP2 mRNA levels were measured with real-time PCR. The PPARγ protein level was measured with immunoblot. C6- and C2-ceramide, but not dihydroC6-ceramide, reduced the expression of PPARγ in a time and concentration dependent manner. The application of 1μM C6-ceramide for 36h reduced PPARγ mRNA level, aP2 mRNA level, and PPARγ protein level to 56.3%, 80.4% and 62.1%, respectively. Since ceramide is known to activate atypical PKC, we also studied the role of atypical PKC on the PPARγ reducing effect. Overexpression of wild type PKCζ magnified and accelerated the effect of TNFα and C6-ceramide on PPARγ mRNA levels, whereas overexpression of dominant negative PKCζ abolished the effect. We also found that the overexpression of constitutive active PKCζ reduced PPARγ mRNA level, aP2 mRNA level, and PPARγ protein level to 61.4%, 70.3% and 81.6%, respectively. Furthermore, TNFα activated nuclear factor-κB (NF-κB), known as a downstream effector of PKCζ to 256.6%, which was enhanced with overexpression of wild-type PKCζ. On the other hand, treatment with phorbol 12-myristate 13-acetate, another activator of NF-κB, also reduced the expression of PPARγ to 57.8%. These results indicate that the reducing effect of TNFα is mediated through ceramide, atypical PKC and NF-κB pathway.