Aim The aim of the present study was to investigate the biochemical characterizations of the lysozyme enzyme for evaluation of its importance in the immune system of the common carp, cyprinus carpio. Materials & Methods In the present study, lysozyme was extracted from the spleen of common carp, cyprinus carpio. Then, partially purified by ammonium sulfate and some properties such as optimum pH and temperature as well as the effects of different salt concentrations of NaCl, MgCl2, KCl, and urea on enzyme activity were evaluated. The enzyme activity was assayed using a suspension of Micrococcus lysodeikticus as a substrate. Findings The optimum pH and temperature were found 4 and 50° C, respectively. Furthermore, lysozyme activity was found to be dependent on salt concentration. Conclusion Based on the results, it’ s been concluded that lysozyme extracted from the spleen of the C. carpio has its optimum activity at high temperature and low pH condition and its activity could be continued with the presence of different salt compounds which all these are related to the environmental conditions of natural habitats of the C. carpio and showed that lysozyme could be one of the key factors of the immune system in this species.