A knife assembly includes a handle, a blade magazine detachably mounted in the handle, and a plurality of blades mounted in the blade magazine. Thus, the blade magazine is released from the handle easily and rapidly, thereby facilitating a user replacing the blades contained in the blade magazine. In addition, the blade magazine is mounted to the handle easily and conveniently, thereby facilitating the user mounting the blade magazine. Further, the blade magazine contains a plurality of blades, thereby facilitating the user carrying the blades.