The aim of this study was to evaluate the antimicrobial activities of several Mannich bases and their derivatives against pathogenic bacteria and fungi. 3-Dimethylamino-1-phenyl-1-propanone hydrochloride (Ig1) as mono-Mannich base, bis(beta-aroylethyl)methylamine hydrochlorides (B1, B5) as bis-Mannich bases, 3-aroyl-4-aryl-1-methyl-4-piperidinol hydrochlorides (C1, C5) as piperidinol derivatives, which are structural isomers of bis-Mannich bases, N,N'-Bis(3-dimethylamino-1-phenylpropylidene)hydra zine dihydrochlorides (D1) as azine derivative of mono-Mannich base Ig1, and some representative quaternary derivatives (Ig4 and C6), which are quaternary derivatives of Ig1 and C1, respectively, have been synthesized. Aryl parts were phenyl in B1 and C1, and 2-thienyl in B5 and C5. Bis-Mannich bases and quaternary Mannich bases were found to be effective antifungal derivatives. Quaternary mono-Mannich base Ig4 has shown twice the amount of higher antifungal potency against the human pathogenic fungus Microsporum canis compared with the reference drug amphotericin-B and it had equal potency against many other fungi species pathogenic in humans and plants. Ig4 was effective against Staphylococcus aureus among the bacteria tested. Preparation of bis-Mannich bases and qua ternization procedure seemed suitable chemical modifications to prepare effective antifungal compounds. Especially quaternary derivatives Ig4, and to some extent C6, seem to be model compounds to develop new antimicrobial agents for further studies.