Xanthone derivatives of the formula (I): ##STR1## (wherein W, X, Y and Z which may be the same or different represent a hydrogen atom, a halogen atom or a lower alkyl group having 1 to 4 carbon atoms; A is hydrogen atom or together with Z forms a --CH.sub.2 -- group which binds to a phenyl carbon adjacent the phenyl carbon to which the oxygen of the group ##STR2## is attached to form a cyclic methylene chain; B is a hydroxymethyl group, a lower alkoxycarbonyl group having 1 to 4 carbon atoms, or a carboxyl group, provided that W is neither a hydrogen atom nor a 7-position methyl group when X, Y and Z are each a hydrogen atom, and A is a hydrogen atom and B is a carboxyl group or a lower alkoxycarbonyl group), as well as non-toxic salts thereof when B is a carboxyl group, and a process for preparing the same are disclosed.The compounds of formula (I) in accordance with the present invention are useful as diuretics having uricosuric activity and can be used in the treatment of edema or hypertension.