Baicalein, a flavonoid, is anti-allergic but only slightly soluble in water. The soluble derivatives of baicalein, disodium baicalein-6-phosphate (BPS) and sodium baicalein-6-sulfate (BSS), were synthesized and examined regarding their effects on hypersensitivity reactions. These derivatives inhibited type I and II reactions as classified by Coombs and Gell. The Arthus reaction belonging to type III reaction, however, was hardly affected with either BPS or BSS. The experimental asthma caused by passive systemic anaphylaxis in guinea pigs was prevented with application of BPS. Thus even by the oral route, BPS appears to be clinically applicable to extensive allergy related diseases.