The association of obesity with type 2 diabetes and insulin resistance has been recognized for decades. However, the mechanism that links obesity and insulin resistance has not been fully elucidated. Recent studies have suggested that the macrophages in the adipose tissue are involved in the association between insulin resistance and obesity. In the present study we co-cultured adipocytes with macrophages and investigated the effect of macrophages on basal and insulin-dependent glucose uptake and serine phosphorylation. An in-vitro co-culture system was developed using differentiated 3T3-L adipocytes and macrophages. Confluent preadipocytes were stimulated with 1µM dexamethazone, 0.5Mm isobutylmethylxanthine and 10µg of insulin. The differentiated adipocytes were identified by lipid accumulation in the form of droplets in the cells . The success of the co-culture was determined by the morphology of the macrophages, which became elongated. Our results demonstrated an increase in the basal uptake of glucose and a decrease in the insulin-dependent uptake of glucose in the co-cultured adipocytes. We also showed a significant increase in serine-307 phosphorylation which prevents the interaction of IRS-1 and IR, resulting in insulin resistance. In order to validate our results, we determined the differential gene expression of the insulin signaling pathway in differentiated adipocytes co-cultured with macrophages, as compared to the differentiated adipocytes cultured alone. The IRS-1 and GLUT-4 genes were down regulated, while GLUT-1 gene was up regulated. : Macrophages that accumulate in the adipose tissue of obese subjects may be one of the risk factors for the development of insulin resistance and type 2 diabetes.