Brown adipocytes and beige adipocytes can expend energy, generate heat, and increase whole‐body energy expenditure. The detailed mechanisms of adipogenesis and thermogenesis of these cells are still obscure. Here, we show that Src family kinases (SFKs) regulate both brown adipogenesis and browning of white adipocytes. To identify factors involved in brown adipogenesis, we first examined the effect of several chemical inhibitors on the differentiation of brown preadipocytes isolated from mouse brown adipose tissue (BAT) and found that treatment with PP2, the specific inhibitor of SFKs, promoted the differentiation. Another inhibitor of SFKs, PP1, also promoted the brown adipogenesis, whereas an inactive analogue of PP2, PP3, did not. Moreover, over‐expression of C‐terminal Src kinase (CSK), the negative regulator of SFKs, also promoted brown adipogenesis. Next, we examined the effect of inhibition of SFKs on the differentiation of white preadipocytes isolated from white adipose tissue (WAT). Our results showed that either PP2 treatment or CSK‐over‐expression generated Ucp1‐positive beige adipocytes, thus inducing browning of white adipocytes. Finally, our analysis showed that the expression levels and activity of SFKs in WAT were much higher than in BAT. These results taken together suggest that SFKs regulate differentiation and browning of fat cells in vivo.