Administration of Tolylsam, a MMP inhibitor with relative specificity for gelatinases, at a dose of 100 mg/kg/day to leptin-deficient (ob/ob) mice kept on high fat diet for 15 weeks, was associated with significantly reduced weight gain as compared to controls (p < 0.0005), resulting in lower body weight (p < 0.0005) at the end of the experiments. Food intake, physical activity and body temperature were not affected. Subcutaneous (SC) (2.9 ± 0.1g vs. 3.4 ± 0.2g in controls; p < 0.05) and gonadal (GON) (3.4 ± 0.1g vs. 3.7 ± 0.1g in controls; p = NS) fat mass were reduced by Tolylsam treatment. Reduced MMP-2 (gelatinase A) activity in adipose tissue extracts was confirmed by zymography. Mild adipocyte hypotrophy was observed in treated SC and GON adipose tissues. Blood vessel density was significantly reduced in Tolylsam treated SC (p < 0.05) and GON (p < 0.005) adipose tissues. Sirius red staining revealed comparable collagen content in both SC and GON fat of treated mice, whereas collagen disorganization (ratio thick/thin fibers) was also similar. Thus, gelatinase inhibition in mice with leptin deficiency resulted in lower body and fat pad weights, associated with mild adipocyte hypotrophy. This indicates that MMP inhibition may impair adipose tissue development independently of leptin.