Tanshinone IIA is known to induce apoptosis in several types of cancer cells. However, little is known about its activity in chemoresistant cells. The aim of this study was to investigate the anticancer properties of tanshinone IIA in cisplatin-resistant human ovarian cancer COC1/DDP cells in vitro. We used a variety of methods to measure cell viability, the resistance index (RI) of cisplatin, cellular apoptosis, p38 mitogen-activated protein kinase (MAPK) expression and phosphorylation, and the mRNA expression of several genes implicated in drug resistance including survivin, Caspase-3, excision repair cross-complementing gene 1 (ERCC1), multidrug resistance (MDR), lung resistance protein (LRP) and glutathione-S-transferase-π (GST-π). We found that tanshinone IIA time- and dose-dependently inhibited the proliferation of COC1/DDP cells and caused significant apoptosis. Western blotting revealed that tanshinone IIA also increased phospho-p38 MAPK in a time- and dose-dependent manner. After treatment by tanshinone IIA for 48 h, the RI of cisplatin and the mRNA expression of survivin, ERCC1 and LRP were all significantly decreased. Furthermore, blockade of p38 signal transduction decreased apoptotic cell rates and dramatically elevated the mRNA expression of the survivin, ERCC1 and LRP genes. We therefore conclude that tanshinone IIA induces apoptosis and reduces cisplatin resistance in COC1/DDP cells and thus causes significant growth inhibitory effects. This mechanism appears to involve p38-mediated downregulation of survivin, ERCC1 and LRP mRNA expression.