An experimental investigation was performed to determine continuous slurry ice making characteristics with water solution in a cooled horizontal pipe to provide fundamental information for a new ice thermal energy storage system. The experiments were carried out under various conditions such as water solution velocity, concentration of water solution, temperature of cooled pipe wall, and pump pressure. In this study, two kinds of cooled pipes were used; one is made of stainless steel tube for making slurry ice and the other is made of glass tube for visualization. The production behavior of the ice particles in the pipe is observed. It was found that the critical condition for continuous ice making was derived as a function of the experimental parameters. Consequently, The relationship between ice making rate and the parameters was clarified.