A new series of benzofuran and benzothiophene derivatives are disclosed. These compounds have a structure which can be obtained by substituting the third position of 2-lower alkyl-benzofuran or 2-lower alkyl-benzothiophene with a substituted benzene derivative, itaconic acid derivative or a substituted phenoxymethyl tetrazole derivative. They are useful as diuretics without side effects of elevating serum uric acid levels and can be used in the treatment of hyperuricemia.