Cancer cachexia (CC) is a multifactorial syndrome with an unknown etiology. The primary symptom is the progressive reduction of the body weight. Recently, down-regulation of adipogenic and lipogenic genes were demonstrated to be early affected during cachexia progression in adipose tissue (AT), resulting in AT remodeling. Thus, this study aimed to evaluate in a co-culture system the influence of the Lewis Lung Carcinoma (LLC) tumor cells (c/c-LLC) in an established pre-adipocyte cell line 3T3-L1 adipogenic capacity. c/c-LLC in the presence of 3T3-L1 caused a reduction in lipids accumulation, suggesting that secretory tumor cells products may affect adipogenesis. Interestingly, a very early (day 2) down-regulation of proliferator-activated receptor gamma (PPARgamma) and CCAAT/enhancer-binding protein alpha (C/EBPalpha), followed by late genes (day 4 and 8), adiponectin, perilipin, and fatty acid-binding protein 4 (FABP4). Caspase-3 expression was increased on the last day of cell differentiation; it occurred in the expression of pro-inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-alpha). Overall, our results suggest that LLC secretory products impair adipocyte differentiation in a co-culture system and increased apoptosis. In summary, our study has shown the inhibition of the adipogenic process in the 3T3-L1 co-culture system with LLC cells.