Pharmaceutical compositions suitable for oral administration comprising paclitaxel, a solvent, a surfactant, a substituted cellulosic polymer, and optionally but preferably a P-glycoprotein inhibitor. The composition may further comprise a diglyceride or mixture of diglyceride and monoglyceride. The composition generates a supersaturated paclitaxel microemulsion upon contact with water resulting in improved oral bioavailability of paclitaxel.