Lipoprotein lipase (LPL) is the rate-controlling enzyme for the accumulation of triacylglycerol into adipocytes, which acts by digesting it into glycerol and fatty acids. In this study, we found that treatment with (+)-JQ1, an inhibitor of the bromodomain and extra-terminal (BET) family proteins, for 4 days from the end of stimulation to induce adipocyte differentiation reduced binding of BRD4, a BET family member, within the gene body of Lpl. This eventually downregulated the expression of Lpl in 3T3-L1 adipocytes. Longer treatment for 8 days reduced the acetylation of histones H3 and H4 within the gene body of Lpl and subsequent Lpl expression. Lpl expression in mesenteric adipose tissues was lower in Brd4 heterozygous mice at 14 days after birth than in wild-type mice at the same age. Furthermore, treatment with an inducer of insulin resistance, tumor necrosis factor-α, reduced BRD4 binding and histone acetylation in the gene body of Lpl and its expression. These results indicate that transcriptional elongation of Lpl controlled by BRD4 may be associated with adipocyte differentiation, and that its suppression is potentially associated with insulin resistance of adipocytes.