Plasticised poly(lactic acid) (PLA)-based antimicrobial films were successfully produced via solvent-casting method. For this purpose, PLA copolymer-bearing quaternary ammonium salt in rate of 5 mol% was successfully fabricated through a two-step reaction procedure, i.e. combination of ring-opening copolymerization and copper(I)-catalysed azide-alkyne cycloaddition click reactions. The synthesized polymer was blended at three different amounts (5, 20 and 30% w/w) with commercial PLA which was plasticized with PEG-1000. After the blending process, antimicrobial activity of all the composite films was investigated against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria via contact-active method. It was determined that the films blended with polymer containing quaternary ammonium salt on its backbone had a highly effective antimicrobial activity against both bacteria, even at the lowest blending rate. Besides, the thermo-mechanical behaviours of obtained films were analysed. Thermal property of films was not changed significantly after blending process of antimicrobial polymer. As a result, it can be said that the film which contains antimicrobial polymer at the lowest amount provides the purpose of this work with the highly effective antimicrobial activity and better mechanical properties compared to other films.