Recently, the topic of biofilm has met a huge interest of researchers owing to a significant role played by this microbial life form in severe infections. These well organised three-dimensional microbial communities are characterized by a strong resistance to antimicrobials. Biofilms significantly contribute to morbidity and mortality as related infections are very difficult to treat due to their tendency to relapse after the withdrawal of antibiotics. According to the literature, antimicrobial peptides (AMPs) have a high potential as future antibiofilm agents. AMPs can influence various stages of biofilm formation and exhibit antimicrobial activity against a broad spectrum of microorganisms including multi-drug resistant strains. The purpose of the present study was to determine the activity of antimicrobial peptides against biofilms formed by a variety of bacterial strains. To do this, the following antimicrobial peptides were synthesized: Citropin 1.1, Lipopeptides Palm-KK-NH2 and Palm-RR-NH2, Omiganan, Pexiganan and Temporin A. Antimicrobial activity of the compounds and conventional antibiotics was determined for planktonic cells and biofilms formed by reference strains of Gram-positive (Staphylococcus aureus, S. epidermidis, Streptococcus pneumoniae, Streptococcus pyogenes) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis) bacteria. AMPs exhibited a strong antibacterial activity against Gram-positive strains, while Gram-negative bacteria were less susceptible. Antimicrobial activity of the tested peptides against biofilms formed by Gram-positive organisms was significantly stronger as compared to that of conventional antimicrobials.