In order to understand the antifungal activity of some derivatives of sanguinarine (S) and chelerythrine (C) and their structure-activity relationships, sixteen derivatives of S and C were prepared and evaluated for in vitro antifungal activity against seven phytopathogenic fungi by the mycelial growth rate method. The results showed that S, C and their 6-alkoxy dihydro derivatives S₁-S₄, C₁-C₄ and 6-cyanodihydro derivatives S₅, C₅ showed significant antifungal activity at 100 µg/mL against all the tested fungi. For most tested fungi, the median effective concentrations of S, S₁, C and C₁ were in a range of 14-50 µg/mL. The structure-activity relationship showed that the C=N+ moiety was the determinant for the antifungal activity of S and C. S₁-S₅ and C₁-C₅ could be considered as the precursors of S and C, respectively. Thus, the present results strongly suggested that S and C or their derivatives S₁-S₅ and C₁-C₅ should be considered as good lead compounds or model molecules to develop new anti-phytopathogenic fungal agents. can't login to work station for 2hrs--took 2 hrs vacation