A disposable microsurgical knife having a blade guard that can be locked into a blade covering position and then easily removed from the knife body prior to introduction to the sterile field is disclosed. The blade guard includes a cylindrical sleeve having a longitudinal slot communicating with a forward open end thereof and terminating in a circumferential notch. The knife body includes a small locking tab formed adjacent a forward tapered portion of the knife. The blade guard is initially assembled on the knife by longitudinally sliding along the knife body from a rear end thereof until the locking tab enters the longitudinal slot assisted by a funnel-shaped leading end for ease of entry. In the blade covering position, simple rotation of the sleeve forces the locking tab into the circumferential notch. For easy removal, reverse rotation of the sleeve causes the tab to re-enter the slot whereupon the sleeve is removed from the knife by sliding rearwardly along the knife body.