The present invention relates to an apparatus for efficiently deodorizing or sterilizing a target space, which is contaminated with virus, bacteria, fungi and the like over a reference value, by using ozone without adversely affecting a human body. More particularly, the present invention relates to an air sterilizer using ozone, which includes a control unit for automatically controlling a proper concentration of ozone capable of efficiently sterilizing the target space according to the size of the target space. Specifically, the air sterilizer comprises an ozone generating unit subjected to ON/OFF control, a control unit for controlling a variety of safety devices having functions of efficiently controlling the concentration of ozone in the target space, a functional air filter unit having functions of cleaning air and removing residual ozone, and a fan for circulating the air in the target space. According to the air sterilizer of the present invention, virus, bacteria and fungi floating in the air can be more efficiently removed over conventional air cleaner and a malodor source can also be eliminated.