The problem of dendrite growth remains unresolved in secondary zinc batteries. In order to improve the cycle life of zinc-secondary batteries, we developed an organic/inorganic composite separator that exhibits an inhibitory effect on short circuits caused by zinc dendrite growth. This separator is designed to have a sufficient ionic conductivity as well as suppression properties for preventing a short circuit. To obtain these performances, inorganic particles and hydrophobic particles are utilized which provide no extra space and no extra electrolyte for dendrite growth. Additionally, this material exhibits a good ionic conductivity.It was also confirmed that the separator we developed provided the carbon-zinc hybrid capacitor with a long life. It was also found that the carbon-zinc hybrid capacitor systems are preferable for evaluating the cyclability of separators used for zinc secondary batteries because the system has a good reproducibility. Consequently, the cycle life using the organic / inorganic composite separator was more than 10 times longer than that of conventional microporous membranes.