Antifungal activity of new copper(II) complexes of 2-methylthionicotinate (2-MeSNic) of the composition Cu(2-MeSNic)2(MeNia)2·4H2O (where MeNia isN-methylnicotinamide), and Cu(2-MeSNic)2(Nia)2·2H2O (where Nia is nicotinamide) and Cu(2-MeSNic)2L2 (where L is isonicotinamide, iNia, or ethyl nicotinate, EtNic) were tested on various strains of filamentous fungi by the macrodilution method. Most sensitive against copper(II) adducts with bioactive ligands wereRhizopus oryzae andMicrosporum gypseum (IC50 1.5–2.3 mmol/L). The adducts with Nia, MeNia and EtNic at 5 mmol/L induced morphological changes in growing hyphae ofBotrytis cinerea, mainly their intensive branching attached to release of cytoplasm with partial growth inhibition. Inhibition of sporulation (>90%) ofAlternaria alternata by Cu(2-MeSNic)2·H2O was observed as a change in the color of the colonies. The highest resistance was marked byB. cinerea andFusarium moniliforme (average IC50 values 4.25 and 3.13 mmol/L, respectively). The presence of all bioactive ligands in copper(II) complexes caused an increase in the inhibition effect against model fungi (except significant inhibition activity of EtNic onR. oryzae).