Objective: Recent studies have identified key transcriptional regulators of brown adipose tissue (BAT) differentiation and function, but posttranscriptional control of this network by microRNAs remains incompletely understood. MiR-33 critically regulates genes involved in metabolic pathways, including cholesterol efflux, reverse cholesterol transport, fatty acid oxidation, and autophagy. Given its role in metabolic homeostasis, we investigated whether miR-33 participates in the regulation of BAT activity, white adipose beiging, and adaptive thermogenesis. Approach and Results: Using primary immortalized brown adipocytes and 10T1/2 cells, we show that miR-33 levels are reduced in brown fat differentiated cells compared with preadipocytes and in response to thermogenic activators. Furthermore, in mice exposed to cold, levels of miR-33 in BAT are rapidly downregulated consistent with a role for miR-33 in repressing adaptive thermogenesis. Using in silico prediction, we identified numerous putative miR-33 target genes in the thermogenic pathway conserved in mice and humans, including regulators of brown adipocyte differentiation and function and mitochondrial activity. We focused our investigation on transcriptional regulators of UCP1 (uncoupling protein 1) and of BAT-enriched genes and demonstrate that miR-33 represses Zfp516 , Dio2 , and Ppargc1a in vitro and in vivo. Treatment of mice with inhibitors of miR-33 increased expression of these miR-33 target genes in brown and subcutaneous white adipose tissue, upregulating expression of UCP1, and rendering mice resistant to cold challenge. Conclusions: Collectively, our findings demonstrate that miR-33 targets key genes involved in BAT activation and white adipose beiging and expand our understanding of how miR-33 coordinately regulates pathways involved in metabolic homeostasis.