A nickel-hydrogen secondary battery is disclosed wherein a long life is assured, an improved self-discharging property in a high temperature storage and the inhibition of increase in inner pressure of the battery in the occasion of over-charging can be realized. The nickel-hydrogen secondary battery comprises, a case (1), a paste-type positive electrode (2) accommodated in the case (1) and containing a nickel oxide and a polymeric binder, a paste-type negative electrode (4) accommodated in the case (1) and containing a hydrogen-absorbing alloy and a polymeric binder, a separator (3) accommodated in the case in so as to be interposed between the positive and negative electrodes (2, 4), and an alkali electrolyte accommodated in the case (1). The separator (3) is formed of a sheet material containing polyolefin-based synthetic resin fibers and has a hydrophilic first surface and a second surface having hydrophilic and hydrophobic portions, the separator (3) is interposed between the positive and negative electrodes with the second surface facing toward the negative electrode (4).