Although the role of bromodomain‐containing protein 4 (BRD4) in ovarian cancer, pancreatic cancer, lymphoma, and many other diseases is well known, its function in cutaneous melanoma is only partially understood. The results of the present study show that the BRD4 inhibitor JQ1 promotes the apoptosis of B16 melanoma cells by altering mitochondrial dynamics, thereby inducing mitochondrial dysfunction and increasing oxidative stress. We found that treatment of B16 cells with different concentrations of JQ1 (125 nmol/L or 250 nmol/L) significantly downregulated the expression of protein subunits involved in mitochondrial respiratory chain complexes I, III, IV, and V, increased reactive oxygen species, induced energy metabolism dysfunction, significantly enhanced apoptosis, and activated the mitochondrial apoptosis pathway. At the same time, JQ1 inhibited the activation of AMP‐activated protein kinase, a metabolic energy sensor. In addition, we found that the mRNA and protein levels of mitochondrial dynamin‐related protein 1 increased, whereas the levels of mitochondrial fusion protein 1 and optic atrophy protein 1 decreased. Mechanistically, we determined that JQ1 inhibited the expression of c‐Myc and altered mitochondrial dynamics, eventually leading to changes in the mitochondrial function, metabolism, and apoptosis of B16 melanoma cells.