Beiging of white adipose tissue (WAT) is capable of adaptive thermogenesis and dissipating energy. The beiging processes have been associated with the increase of anti-inflammatory M2 macrophages, however the function of M2 macrophage on beiging and the underlying mechanism are not fully understood. Here we identified a macrophage cytokine Slit3 by analyzing the transcriptome of M2 macrophages collected with FACS in inguinal WAT (iWAT) of mice after cold exposure. Once released from macrophages, Slit3 bound to the ROBO1 receptor on sympathetic neuron and activated tyrosine hydrolase (TH) through PKA and CaMKⅡ signaling, and thus stimulated norepinephrine (NE) synthesis and release. NE acts on adipocytes and stimulate thermogenesis. Adoptive transfer of Slit3-overexpressing M2 macrophages to iWAT depot acquired local adipocytes with beiging phenotype and enhanced thermogenesis. In addition, mice bearing the myeloid inactivation of Slit3 were cold intolerant and gained more weight due to the lowered metabolic rate. Collectively, we demonstrate Slit3 is a macrophage cytokine and promotes beiging and thermogenesis through intensifying the sympathetic nerve function. As the expanded M2 macrophages are integral cell population in adipose tissue, the macrophage-Slit3-sympathetic neuron-adipocyte axis assures the long-term cold adaption.