Abstract: A knife holder for a utility knife is disclosed comprising an elongated case forming a blade opening at the forward end and an interior guide for guiding a blade carrier and a blade carrier adapted for mounting a blade and being slidably mounted to the guide for selective longitudinal movement between a retracted sheathed position and an extended unsheathed position. The blade carrier has outwardly extending flanges for supporting a blade and a retainer tab for laterally retaining the rearward portion of the blade and the case has a retainer protrusion at the blade opening for laterally retaining the forward end of the blade so that the retainer tab and the retainer protrusion coact to retain the blade to stabilize the blade during usage.