Intramuscular fat, which is closely related to the traits of tenderness, juiciness, and flavor of pork, is regulated by numerous molecular regulatory mechanisms that have been regarded as an important agricultural research area. Long noncoding RNAs (lncRNAs) are emerging regulators involved in adipogenesis due to their functional diversity. In this study, we identified a novel lncRNA related to porcine adipogenesis, named lncIMF1, based on previous RNA sequencing results. Our results suggested that lncIMF1 was most abundantly expressed in adipose tissue and located in both the cytoplasm and nucleus. Besides, lncIMF1 promoted the proliferation and differentiation, while inhibited apoptosis of intramuscular preadipocytes. Moreover, lncIMF1 could act as a molecular sponge for miR-187, inhibiting the binding of miR-187 and SMAD1, thereby promoting the expression of SMAD1 and enhancing the adipogenic differentiation of intramuscular preadipocytes. Additionally, we found that lncIMF1-miR187-SMAD1 axis could activate the p38-mitogen-activated protein kinase (MAPK) pathway. Taken together, our study provided new insights into the role of lncRNAs in the regulation of pork quality.