With a view to constructing a resource circulation system for lithium ion batteries, we attempted to recover lithium and cobalt ions by hydrothermal citric acid leaching into water. Under reaction conditions in the range of 100-200 degrees C, 5-30 min, and 0.1-1.0 M citric acid, leaching efficiency of lithium and cobalt was found to increase with reaction temperature, time and citric acid concentration, and recovery of both metals exceeded 80%. To elucidate the reaction mechanism, leaching rate constants of lithium and cobalt were calculated based on the unreacted core or shrinking core model. It was found that the leaching behavior was expressed by the product layer controlled model in the unreacted core model, and the leaching rate constants of lithium and cobalt are approximately linearly dependent on the proton concentration.