It is intended to provide a medicinal composition having a high biological availability and a process for producing the same which comprises dispersing a drug component in two or more surfactants (for example, surfactants belonging to the same series such as a long-chain fatty acid glyceride having a long-chain polyoxyethylene in its hydrophilic group with a medium-chain fatty acid glyceride having a short-chain polyoxyethylene in its hydrophilic group), adding a small amount of water thereto to give a semisolid or liquid medicinal composition in the form of a microemulsion, and producing an oral preparation such as capsules by using the same so as to form and sustain a stable microemulsion containing the drug component (in particular, a hardly water-soluble drug component) in the digestive tract.