Bariatric surgery remains the only effective treatment for morbid obesity. Sleeve gastrectomy (SG) has recently increased in popularity and is associated with 60-80% excess weight loss; however, the mechanisms underlying SG-mediated weight loss are unclear. Diet-induced obese male Sprague-Dawley rats (n=58) were either sham-operated or underwent SG and had ad libitum access to food. A subset of sham-operated rats was pair-fed to the food consumed by the SG group. The first cohort (n= 23) were used to establish the rodent model of SG in our hands and detail its impact on metabolic parameters. Body composition was assessed using DEXA prior to surgery and at the end of 30 or 34-day treatment. Food intake and body weight were monitored daily. Rats were also housed in indirect calorimetry cages for the assessment of oxygen consumption and carbon dioxide production. To further elucidate the contribution of energy expenditure, particularly in brown adipose tissue (BAT), to SG-induced weight loss, a second cohort of animals (n=22) were implanted with biotelemetry devices between the interscapular lobes of BAT to assess local changes in BAT temperature. In a third cohort (n= 13), neuronal activation, indicated by elevated Fos protein in the nucleus of the solitary tract (NTS), was assessed in response to SG. In all cohorts, SG caused a significant reduction in both body weight and cumulative food intake (P<0.0001) with commensurate reductions in fat mass (P<0.001), fat percentage (P<0.05) and lean mass (P<0.05) compared to sham surgery. Importantly, SG was associated with an increase in BAT thermogenesis, demonstrated by an elevation in BAT temperature (P<0.0001) and UCP1 expression (P<0.001). Whole body oxygen consumption was not different between sham-operated and SG animals. SG significantly elevated Fos expression in the NTS compared to sham surgery (P<0.05). These data support a role for BAT thermogenesis in SG-mediated weight loss.