The basic purpose of the JIT(Just In Time) production system is to increase profits by reducing costs-that is, by completely eliminating waste such as excessive stocks or workforce. To achieve cost reduction, Production must promptly and flexibly adapt to changes in market demand without having wasteful slacks. :iuch an ideal is accomplished by the concept of JIT, producing the necessary items in the necessary quantities at the necessary time. The JIT production system is supported by the following: reduction of setup time, smoothing of production, standardization of jobs, improvement activities, design of machine layout, Kanban system, autonomation etc. This study examined the present state of the domestic JIT production system and introduced the empirical case of JIT application a small and medium manufacturing company. A synthetic resins manufacturing company applied JIT principles to its processes and achieved the great performance.