Mycelial growth inhibition activity of forty-one N-substituted phenyl 5-chloro-1,3-dimethylpyrazole-4-carboxamides against Rhizoctonia solani was analysed quantitatively by multiple regression analysis using physicochemical parameters of substituents as independent variables and pEC_(50) as dependent variable. As a result, a quantitative structure-activity relationship was formulated using eight physicochemical parameters, which explains 83% of variance of the fungicidal activity. The most important parameter for the biological activity was log k′, as related to the penetration and transport processes in the biological system. The activity also correlated with other hydrophobic parameters(π₂, π₃), an electronic parameter(∑σ), and steric parameters(STERIMOL parameters L₃, L₄).