Recently, ice-on-coil type ice storage system has become a very popular issue in application to electric powered air conditioning systems. An experimental study has been carried out to investigate the ice making characteristics of an ice-on-coil type ice storage system. The ice storage system used two rectangular tank, one is 900 ℓ with a thermal capacity 3,300 kcal/h and the other is 3,000 ℓ with a thermal capacity 9,900 kcal/h. An experimental data has been measured as the variation of a ice making time. The results indicate that the ice making rate increase due to variation of ice making time gradually, and is high in case of the smaller refrigerant coil from 5 hour but larger refrigerant coil after this.