Adequate nutrient intake is critical in the maintenance of normal physiologic activity of rodents in biomedical studies. Vitamin K is an essential nutrient in rodent diets and functions as a cofactor for the gamma-carboxylation of various proteins involved in blood coagulation and bone metabolism. Several forms of vitamin K are used in rodent diets, with a shift during the last decade towards the use of phylloquinone, the predominant form in human diets, and a concomitant increase in concentrations. This review summarizes current recommendations for vitamin K in rodent diets relative to our evolving knowledge about this fat-soluble vitamin.