Brown adipose tissue (BAT) is known to dissipate chemical energy in response to cold or excess feeding and modulate energy balance. The study aimed to test the hypothesis that BAT is fundamental to glucose homeostasis regulation. Researchers transplanted BAT from male donor mice into the visceral cavity of age- and sex-matched recipient mice. By 8–12 weeks post-transplantation, recipient mice showed improved glucose tolerance, increased insulin sensitivity, lower body weight, decreased fat mass, and a complete reversal of high-fat diet-induced insulin resistance. Increasing the amount of transplanted BAT further enhanced these metabolic effects. BAT transplantation increased insulin-stimulated glucose uptake in endogenous BAT, white adipose tissue (WAT), and heart muscle but not skeletal muscle. The improved metabolic profile was lost when the BAT used for transplantation was obtained from Il6-knockout mice, indicating that BAT-derived IL-6 is crucial for the profound effects of BAT transplantation on glucose homeostasis and insulin sensitivity. These findings highlight a previously underappreciated role for BAT in glucose metabolism.Brown adipose tissue (BAT) is known to dissipate chemical energy in response to cold or excess feeding and modulate energy balance. The study aimed to test the hypothesis that BAT is fundamental to glucose homeostasis regulation. Researchers transplanted BAT from male donor mice into the visceral cavity of age- and sex-matched recipient mice. By 8–12 weeks post-transplantation, recipient mice showed improved glucose tolerance, increased insulin sensitivity, lower body weight, decreased fat mass, and a complete reversal of high-fat diet-induced insulin resistance. Increasing the amount of transplanted BAT further enhanced these metabolic effects. BAT transplantation increased insulin-stimulated glucose uptake in endogenous BAT, white adipose tissue (WAT), and heart muscle but not skeletal muscle. The improved metabolic profile was lost when the BAT used for transplantation was obtained from Il6-knockout mice, indicating that BAT-derived IL-6 is crucial for the profound effects of BAT transplantation on glucose homeostasis and insulin sensitivity. These findings highlight a previously underappreciated role for BAT in glucose metabolism.