A stable, nonsublimable γ-cyclodextrin inclusion complex of menadione (Vitamin K3) of 11.7% menadione content (molar ratio 1:1) was prepared in solution, in suspension, and by ‘kneading’. The physicalchemical properties of the complex formed were studied by X-ray diffraction, by thermal analysis (DTG, TG, DSC, TEA), and by chiroptical studies. The biological activity of the complex was tested on baby chickens by prothrombin time determination. Reduced prothrombin times showed an enhanced bioavailability of menadione in complexed form. The stability of vitamin K3 is greatly improved in pharmaceuticals or in veterinary products prepared with a menadione-γ-CD inclusion complex.