Propofol (PRO) is a hypnotic used to induce and maintain general anesthesia. A risk of drug–drug interactions exists in cases of clinical co-administration of PRO and midazolam (MDZ) or carbamazepine (CBZ). Therefore a sensitive and rapid assay is needed to monitor these drugs. In this study, a sensitive and selective liquid chromatography-tandem mass spectrometry technique was developed for simultaneous determination of PRO, MDZ, and CBZ in plasma. Simultaneous selected reaction monitoring in the positive and negative ionization modes was used for mass detection. Analytes were isolated from plasma samples by a simple, economic, and rapid solid-phase extraction method. Chromatographic separations were achieved using a Chromolith Performance RP-18e analytical column (100×4.6 mm i.d.) with a mixture of acetonitrile–ammonium acetate buffer (10 mM, pH 3.5) (90 : 10, v/v) as the mobile phase. The method was fully validated for PRO, MDZ, and CBZ over concentrations ranging at 1–100, 2–100, and 7–1000 ng/mL, respectively, with acceptable validation parameters. Furthermore, the method was applied to monitor PRO and MDZ or CBZ following co-administration in rats.