Heat production mediated by Brown Adipose Tissue (BAT) is important for defense against cold and maintenance of whole-body energy balance. To assess the role of ERAD in BAT, we generated adipocyte-specific Sel1L-deficient mice. These knockout animals were sensitive to acute cold exposure and strikingly, brown adipocytes from the knockout mice exhibited altered mitochondrial morphology. This study will establish the importance of ERAD in mitochondrial function and dynamics of brown adipocytes. Moreover, as BAT-mediated thermogenesis is targeted in the treatment of obesity and type 2 diabetes, this study may reveal novel regulators or targets to modulate BAT function under physiological and pathological conditions.