The invention relates to an energy-saving ventilator for ventilating inside and outside an air conditioner room. The energy-saving ventilator comprises an enclosure (10), a heat exchange core (30), an air exchange device (40) and an electric control component (50), wherein the wall of the enclosure (10) is provided with a fresh air port (11) and an exhaust port (14) communicated with the outside and an air supply port (12) and an air return port (13) communicated with the inside; and through the air exchange device (40), the fresh air entering from the fresh air port and the polluted air entering from the air return port alternately exchange heat through each part of the heat exchange core from the opposite direction, and then are delivered into the inside through the air supply port and exhausted to the outside through the exhaust port. The energy-saving ventilator is characterized in that the heat exchange core is air filter cotton made of a fiber material, wherein heat exchange core contains a phase change substance of which the phase change temperature is between the indoor temperature and the outdoor temperature of the air conditioner room, the phase change substance is phase change salt or phase change polymer, and the phase change substance is added into the fiber material by using a filling method or a padding method, a microcapsule blending method or a microcapsule glue spraying method. The energy-saving ventilator has the advantages of high heat exchange efficiency, low cost, easy cleaning, long service life and capability of purifying air, so the energy-saving ventilator can be widely applied to various buildings and serve as an ideal energy-saving ventilating device for the environment-friendly energy-saving affairs.