Disclosed in this invention is an adjuvant formulation for enhancing the fungicidal efficacy of KNF-1001 or KNF-1002 against plant diseases comprising an adjuvant selected from the group consisting of a polyoxyethylene-based nonionic surfactants which has an aliphatic alcohol, a fatty acid or triacyl glyceride as a lipophilic moiety containing at least 8 carbon atoms and a polyoxyethylene as a hydrophilic moiety having 3 to 25 oxyethylene repeating units, a polyoxyethylene and 25 to 45 oxypropylene repeating units and a mixture thereof, an anionic surfactant selected from the group consisting of sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate and a mixture thereof, and fatty acid alkyl esters having at least 14 carbon atoms. Also disclosed in this invention is a fungicidal composition for enhancing the fungicidal efficacy of KNF-1001 or KNF-1002 against plant diseases, which comprises a selected active compound together with said adjuvant.