The present invention relates to microbicides for agricultural or horticultural use containing sulfonamide derivative of, for example, a formula (I): or a salt thereof, [wherein A<1 >is (1) an
aryl group which may be substituted or (2) a heterocyclic group which may be substituted, X<1 >is (1) a
chemical bond, (2) a
methylene group which may be substituted, or (3) a
vinylene group which may be substituted, B<1 >is a five-membered heterocyclic group comprising
nitrogen or
sulfur atoms as the ring-constructing atoms except for carbon atoms and may be substituted or a condensed heterocyclic group which may be substituted, Z<1 >is (1) a
hydrocarbon group which may be substituted, (2) an
acyl group which may be substituted, (3)
formyl group, (4) an amino group which may be substituted, (5) a group represented by -N=CR<1>R<2 >(wherein each of R<1 >and R<2 >is a
hydrogen atom or a
hydrocarbon group which may be substituted), (6) a cyclic amino group, (7) a group represented by -OR<3 >(wherein R<3 >is a
hydrogen atom, a
hydrocarbon group which may be substituted, an
acyl group which may be substituted,
formyl group or an alkylsulfonyl group which may be substituted) or (8) -S(O)nR<4 >(wherein n stands for an integer from 0 to 2, R<4 >stands for a
hydrogen atom or a hydrocarbon group which may be substituted). The said compounds or the salts thereof are sulfonamide derivatives with microbicidal action, are useful as excellent microbicides for agricultural or horticultural use, because they are safe, and they have little influence on human beings, farm animals,
natural enemies, or the environment, and exert excellent control effects even on resistant microbes.