Antimicrobial polymers based on polyacrylonitrile (PAN) have been prepared. The cyano groups of the polyacrylonitrile were modified through the reaction with different aliphatic diamines having varied chain lengths. Formation of biocidal polymers (antifungal and antibacterial agents) containing quaternary ammonium salts were then achieved by immobilization of glycidyl trimethyl ammonium chloride (GTMAC) onto the amine-terminated polymers. Antimicrobial activity of the prepared polymers was demonstrated against some selected plant and human pathogenic Gram-negative and Gram-positive bacteria, as well as some pathogenic fungi by the cut plug method and viable cell counting methods. Generally, all polymers showed an increase in the inhibitory action against all the tested microorganisms in comparison with their control.