Abstract: Objective To observe the effect of medium-chain fatty acids on cholesterol efflux in THP-1 macrophages-derived foam cells. Methods WST-1 were used to detect the effect of different fatty acids (in the presence of 200 μmmol/L) on the cell viability of THP-1, including caprylic acid (C8∶0), capric acid (C10∶0), myristic Acid (C14∶0), palmitic acid (C16∶0), stearic acid (C18∶0), oleic acid (C18∶1), linoleic acid (C18∶2) and alpha linolenic acid (C18∶3). The cell model of cholesterol efflux that mediated by ApoA1 was established. Different fatty acids (0 μmmol/L, 100 μmmol/L and 200 μmmol/L) were used to intervene the THP-1 macrophages-derived foam cells of enriched ³H-cholesterol, then after 24 hours, the rate of cholesterol efflux were determined by the liquid scintillation. Results In the presence of 200 μmmol/L, different fatty acids showed no adverse effect on the viability of THP-1 cell line (P＞ 0.05). Compared with the blank group, ApoA1 mediated cholesterol efflux was significantly higher (P＜ 0.05). With the increase of concentration of fatty acids, C8∶0, C18∶0, C18∶2 and C18∶3 showed significant effects on cholesterol efflux (P＜ 0.05). In the concentration of 200 μmmol/L, C8∶0 and C18∶3 fatty acids significantly promoted cholesterol efflux comparing with control group (P＜ 0.05), furthermore, C8∶0 fatty acid promoted cholesterol efflux was significantly higher than in C10∶0, C14∶0, C16∶0, C18∶0, C18∶1 and C18∶2 fatty acids groups (P＜ 0.05). Conclusion The medium-chain fatty acid C8∶0 can increase cholesterol efflux in THP-1 macrophages-derived foam cells and is obviously higher than that of other fatty acids when its concentration is 200 μmmol/L.