The transcription factor carbohydrate response element binding protein (ChREBP) mediates insulin-independent, glucose-stimulated gene expression of multiple liver enzymes responsible for converting excess carbohydrate to fatty acids for long-term storage. To investigate ChREBP's role in the development of obesity and obesity-associated metabolic dysregulation, ChREBP-deficient mice were intercrossed with ob/ob mice. As the result of deficient leptin expression, ob/ob mice overeat; they become obese, resistant to insulin, and display marked elevations in hepatic lipogenesis, gluconeogenesis, and plasma glucose and triglycerides. Messenger RNA expression of all hepatic lipogenic enzymes was significantly lower in ob/ob-ChREBP-/- than ob/ob mice, resulting in decreased hepatic fatty acid synthesis and normalization of plasma free fatty acid and triglyceride levels. Overall weight gain in addition to adiposity was reduced in the doubly-deficient mice. The former was largely attributable to decreased food intake and may result from decreased hypothalamic expression of the appetite-stimulating neuropeptide, Agouti-related protein. Messenger RNA expression and activity of gluconeogenic enzymes also was lower in the doubly-deficient mice, contributing to significantly lower blood glucose levels. The results of this study suggest that inactivation of ChREBP expression not only reduces fat synthesis and obesity in ob/ob mice but also results in improved glucose tolerance and appetite control.