The aim of this work was to examine the in vivo and in vitro effects of NP on Bax and Caspase-3 expressions in 3T3-L1 preadipocytes and adipose tissue of rats. Forty rats were gavaged with NP for 24 weeks at the doses of 0.02 μg/kg, 0.2 μg/kg, 2.00 μg/kg and groundnut oil, respectively. 3T3-L1 preadipocytes were exposed to NP (0, 40 pM, 40 nM, 40 μM) during the stages of the MDI-induced differentiation. The expression of apoptotic protein Bax and Casapse-3 was both up-regulated in all NP treatment groups than that in the control. Oil Red O staining of 3T3-L1 preadipocytes exposed to 40 μM NP showed that the whole field of view was the reddest, and new lipid droplets were observed. At the late stage of differentiation, the expression of Caspase-3 protein at high dose of NP group was higher than that of the control group. Simultaneously, the protein expression of Bax decreased at the late stage. Subchronic exposure of NP could increase the body weight and expression of Bax and Caspase-3 in adipose tissue of rats. The accumulation of lipid droplets and increased expression of Bax and Caspase-3 in 3T3-L1 preadipocytes after NP exposure were revealed as well.