Biofilm formation of Listeria monocytogenes in food processing environments cause potential source of cross-contamination to foodstuffs; hence, the control of biofilm is currently addressed to find effective solutions for preventing biofilm formation or eliminating the established one. Forty-five strains of Listeria monocytogenes isolated from Pangasius fish-processing plants were studied for their capability to form a biofilm on 96-well microtiter plate by using the conventional crystal violet staining. Additionally, the inhibitory effect of biofilm formation by food additives including monascus pigment and ε-polylysine was examined. The average OD value showing biofilm mass of all 45 strains L. monocytogenes increased with an increasing temperature and time (p < 0.05). Monascus pigment and ε-polylysine significantly decreased biofilm formation by 80 ± 5.5% and 20 ± 5.9%, respectively, at the tested concentration (p < 0.05) Further, the effects of lysozyme (0.1 mg/mL) alone or in combination with slightly acidic hypochlorous water (SAHW) with 40 mg/L available chlorine or sodium hypochlorite (NaOCl) with 100 mg/L available chlorine against 7-d established biofilm of L. monocytogenes were investigated. The results indicated that slightly acidic hypochlorous water alone exhibited significant antibacterial activity (p < 0.05), decreasing the viable count by 5.2 ± 0.5 log CFU/mL. It seems that sequential treatment of lysozyme and SAHW showed an additional efficacy against biofilm of L. monocytogenes on polystyrene plate surface, reducing 70% of biomass of biofilm and 7.6 ± 0.3 log of biofilm viable cells (p < 0.05). Additionally, SAHW exhibited greater bactericidal activity against viable biofilm cells than NaOCl did. This result reveals that SAHW is a promising disinfectant agent against L. monocytogenes and the potential alternative to NaOCl in practice.