Serratia marcescens CK-3, decomposing chitin which is a major component of cell wall in phytopathogenic fungi, was isolated from the continuous cropping rhizosphere of pepper and cucumber and its enzymatic property was examined. S. marcescens CK-3 was found to have antagonistic effects against Fusarium axysporum and Rhizoctania solani and to have complex enzyme systems such as chitinase, laminarinase, and proteinase. The preferable composition of the medium for production of chitinase was found and was as follows : colloidal chitin 1.5%, tryptone 0.5%, glucose 1.0%., peptone 0.2%, MgSO₄·7H₂O 0.1 %, K₂HPO₄ 0.1 %, and NaCl 0.1 % (w/v), pH 6.8. The maximum enzyme production was observed after culture of 72 hours at 30℃ using a medium containing the above chemical composition. The optimal pH and temperature for in vitro activity of chitinase from S. marcescens CK-3 were pH 7.5 and 50℃, respectively. The enzyme activity increased by metal ions such as Ag^+ and Mn^(++).