This study aimed at investigation of the dipping effects of chitosan and nano chitosan (chitosan nanoparticles) (with particles sizes of 37, 78, and 222 nm) on extension of the shelf life of fresh tilapia fish (Oreochromis niloticus) at chilling storage. In addition, the effects of the chitosan and its nanoparticles on improvement of the microbiological quality of tilapia were further examined via evaluation of the hygiene indicators (total bacterial count, total psychrophilic count, and total mould and yeast counts). Furthermore, the effects of the chitosan and its nanoparticles against specific foodborne pathogens including Staphylococcus aureus, E. coli, Salmonella Typhimurium, Vibrio parahaemolyticus and Aspergillus flavus were screened. The obtained results indicated that chitosan nanoparticles were effective for elongation of the shelf life of tilapia, particularly chitosan nanoparticles with particle size of 37 nm. In addition, chitosan and its nanoparticles had significant antimicrobial effects either against the hygiene indicators, or foodborne-specific pathogens. In conclusion, the use of chitosan and its nanoparticles is highly recommended to extend the shelf life and improve the microbiological quality of tilapia fish.