Conjugated linoleic acid (CLA), which is a generic term to describe isomers of octadecadienoic acid, has been reported to exert various beneficial physiological effects. Accumulating data show that CLA, especially trans10, cis12 (t10, c12)-CLA, has a potent body fat-reducing effect, which is prominent in mice and to a lesser extent rats. In addition, several clinical studies have demonstrated the body fat- and weight-reducing effect of CLA in humans. However, t10, c12-CLA evokes severe lipodystrophy in mice that results in impaired glucose metabolism. Therefore, while CLA is a promising agent for the amelioration of obesity and obesity-related diseases, it is important to establish its safety prior to common use in humans. In addition, it is important to elucidate the details of the molecular mechanisms of CLA. Here, we focus on the response of adipocyte to CLA.