The invention relates to a self-microemulsifying drug delivery system ("SMEDDS") of mitotane, with enhanced bioavailability. More particularly the invention provides a mitotane oily formulation comprising propylene glycol monocaprylate (10 to 30% w/w), propylene glycol dicaprate (20 to 60% w/w) and polyoxyethylenesorbitanne monooleate (10 to 30% w/w).