An air bearing assembly for supporting a running web in a paper slitting apparatus is particularly adapted for use in slitting a corrugated paperboard web and includes a flat web-supporting plate which is slotted to receive a thin annular slitting blade rotatably supported above the web. The flat supporting plate includes a series of apertures for directing a flow of compressed air upwardly through the plate to support the web on an air bearing or cushion as it travels over the plate and through the slitting blade. The air apertures are preferably concentrated along the edges of the slot. The slot is contoured to the shape of the cross sectional profile of the blade such that the slot tapers to an upstream point where the blade passes through the web and into the slot and where blade load on the web is greatest. Additional air bearing support may be provided at this point as well, and across the entire supporting surface of the plate.