Background: Chitosan, a biodegradable polymer with no toxicity, has also been targeted as a DNA vector. In this study, the effects of lysozyme on chitosan / plasmid nanoparticles were investigated. Methods: In this study, the gelation method was used to make nanoparticles. After studying the percentage of plasmid loading in chitosan nanoparticles and also the Nanoparticle properties, the nanoparticles were treated with lysozyme and the effects of enzymatic digestion were investigated. Results: The results of this study showed that the percentage of plasmid loading in the nanoparticles was 100%. The size, dispersion index, and zeta potential of the nanoparticles were 173 nm, 0.292 and 10.08 mV, respectively. the results of enzymatic digestion showed that the solution containing lysozyme at concentration of 10 µg / ml and enzymatic power of 100 u / ml after 4 hours was able to partially digest chitosan nanoparticles but did not completely release the plasmid. but after 24 hours, it releases the plasmid completely from the nanoparticles. Conclusion: By reviewing the results of this study and comparing it with the findings of other studies on chitosan, it is found that in addition to optimal conditions for lysozyme enzyme function, the time factor is also important for lysozyme function in complete release of DNA from chitosan / plasmid nanoparticles.