Diaporisoindole B (DPB), an isoprenylisoindole alkaloid isolated from the mangrove endophytic fungus Diaporthe sp. SYSU-HQ3, has been proved to have a good anti-inflammatory activity in macrophage cells. In this study, we found that DPB was able to reduce lipid accumulation in THP-1 macrophage-derived foam cells. DPB could inhibit the lipid influx-related gene CD36 and increase the expression of lipid efflux-related genes ATP binding cassette transporter A1 (ABCA1), ATP binding cassette transporter G1 (ABCG1), and scavenger receptor B1 (SR-B1). Moreover, DPB elevated low-density lipoprotein receptor (LDLR) protein expression in HepG2 cells, which can increase the transport of LDL. Meanwhile, DPB could downregulate the expression levels of proteins related to cholesterol and fatty acid synthesis. Further study showed that DPB could activate peroxisome proliferator-activated receptor gamma (PPARγ) and inhibit mitogen-activated protein kinase (MAPK) phosphorylation. Taken together, our findings demonstrated that DPB could reduce lipid accumulation in THP-1 macrophage cells by reducing the intake of lipids and promoting the efflux of lipids and also could promote the reverse cholesterol transport (RCT) mechanism by upregulating SR-B1 and LDLR in HepG2 cells.