ATP-sensitive potassium channels (KATP channels) play an important role in insulin secretion from pancreatic beta cells. We have investigated the effect of propofol on KATP channels in cultured single pancreatic beta cells of rats. Channel activity was recorded from membrane patches using the patch-clamp technique. In the inside-out configuration bath-applied propofol inhibited the KATP channel activities in a dose-dependent manner. The half-maximal inhibition dose (ED50) was 48.6⁑8.4μM and the Hill coefficient was 0.73⁑0.11. Single channel conductance calculated from the slope of the relationship between single channel current and pipette potential (⁢20∼⁢100 mV) was not significantly altered by propofol (control: 60.0⁑2.7 pS, 0.1 mM propofol: 58.7⁑3.5 pS). However, mean closed time was surely increased. Above results indicate that propofol blocks the KATP channels in the pancreatic beta cells in the range of its blood concentrations during anesthesia, suggesting a possible effect on insulin secretion and blood glucose level.