This study investigated whether KMUP-1, a xanthine-based derivative, inhibits L-type Ca2+ currents (ICa,L) in rat basilar artery smooth muscle cells (RBASMCs). We used whole cell patch-clamp recording to monitor Ba2+ currents (IBa) through L-type Ca2+ channels (LTCCs). Under voltage–clamp conditions, holding at –40 mV, KMUP-1 (1, 3, 10 μM) inhibited IBa in a concentration-dependent manner and its IC50 value was 2.27±0.45 μM. A high concentration of KMUP-1 (10 μM) showed without modifying the IBa current–voltage relationship. On the other hand, the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA, 1 μM) increase IBa was inhibited by KMUP-1. Pretreatment with the PKC inhibitor chelerythrine (5 μM) intensified KMUP-1-inhibited IBa. However, the Rho kinase inhibitor Y-27632 (30 μM) failed to affect the IBa inhibition by KMUP-1. In light of these results, we suggest that KMUP-1 inhibition of LTCCs in concentration- and voltage-dependent manners in RBASMCs may be due, at least in part, to its modulation of the PKC pathway.