Our previous study indicated that oleic acid prevented apoptotic cell death induced by trans10, cis12 (t10, c12)-conjugated linoleic acid in rat hepatoma dRLh-84 cells. The intracellular mechanism of action oleic acid is still unknown. Here, we showed that p38 mitogen-activated protein kinase (MAPK) inhibition using its specific inhibitor SB203580 cancelled the ameliorative effect of oleic acid on the cytotoxicity of t10, c12-conjugated linoleic acid. In addition, SubG1 cell population analysis showed that p38 MAPK played an essential role in the prevention of apoptotic cell death by oleic acid. In fact, p38 phosphorylation level was upregulated in cells treated with oleic acid irrespective of t10, c12-conjugated linoleic acid stimulation. Interestingly, t10, c12-conjugated linoleic acid increased intracellular triglyceride accumulation. However, oleic acid completely inhibited this effect. These observations indicated the involvement of blockade of a p38 MAPK pathway in the ameliorative effect of oleic acid on apoptosis induced by t10, c12-conjugated linoleic acid.