Glucosamine salts and derivatives are effective for the improvement of blood flow, and hence, for the prevention and/or treatment of diseases caused by blood flow disturbances, such as thrombosis. Use of glucosamine salts or glucosamine derivatives as active ingredients can provide blood flow improvers, thrombosis preventives or remedies, and dietetic drinks or foods for the improvement of blood flow or for the prevention and/or treatment of thrombosis. Administration of glucosamine salts or glucosamine derivatives can improve blood flow and can prevent and/or treat thrombosis.