The purpose of this study was to investigate the effect of atorvastatin, HMG-CoA reductase inhibitor, on the pharmacokinetics of diltiazem and its active metabolite, desacetyldiltiazem, in rats. Pharmacokinetic parameters of diltiazem and desacetyldiltiazem were determined in rats after oral administration of diltiazem $(15mg{cdot}kg^{-1})$ to rats pretreated with atorvastatin $(0.5;or;2.0mg{cdot}kg^[-1})$. Compared with the control (given diltiazem alone), the pretreatment of atorvastatin significantly altered the pharmacokinetic parameters of diltiazem. The peak concentration $(C_{max})$ and the areas under the plasma concentration-time curve (AUC) of diltiazem were significantly $(p<0.05,;0.5mg{cdot}kg^{-1};;p<0.01,;2.0mg{cdot}kg^{-1})$ increased in the presence of atorvastatin. The AUC of diltiazem was increased by 1.40-fold in rats pretreated with $0.5mg{cdot}kg^{-1}$ atorvastatin, and 1.77-fold in rats pretreated with $20mg{cdot}kg^{-1}$ atorvastatin. Consequently, absolute bioavailability values of diltiazem pretreated with atorvastatin (8.4-10.6%) were significantly higher (p<0.05) than that in the control group (6.6%). Although the pretreatment of atorvastatin significantly (p<0.05) increased the AUC of desacetyldiltiazem, metabolite-parent AUC ratio (M.R.) in the presence of atorvastatin $(0.5;or;2.0mg{cdot}kg^{-1})$ was significantly decreased compared to the control group, implying that atorvastatin could be effective to inhibit the metabolism of diltiazem. In conclusion, the concomitant use of atorvastatin significantly enhanced the oral exposure of diltiazem in rats.