Recent studies have shown that medium-chain triacylglycerol (MCT) improved serum albumin concentration in elderly people with protein-energy malnutrition (PEM) and in malnourished rats. However, the mechanism for this effect has not been clarified. Dietary MCT promotes insulin secretion from the pancreas, and insulin activates mammalian target of rapamycin (mTOR) complex 1 (mTORC1) via the activation of phosphoinositide 3-kinase (PI3K) and its downstream effecter, Akt. mTORC1 promotes mRNA translation through S6K and 4E-BP1. Therefore, we hypothesized that dietary MCT elevates albumin synthesis through promotion of insulin-Akt-mTOR transduction in the liver. To test this hypothesis, we measured phosphorylated Akt, mTOR and albumin in the livers of malnourished rats. In the present study we examined rats fed low-protein diets containing either MCT or long-chain triacylglycerol (LCT) with energy restriction. The plasma and liver albumin levels were significantly higher in the MCT-fed group than in the LCT-fed group. In addition, plasma insulin concentration, liver phosphorylated Akt/Akt and phosphorylated mTOR/mTOR levels were significantly higher in the MCT-fed group than in the LCT-fed group. These results suggest that one of the mechanisms for the albumin improvement effect of dietary MCT is the promotion of albumin synthesis through the insulin-Akt-mTOR signaling pathway of the liver.