To provide a positioning structure of a slide basket for a knockdown rack, capable of easily fixing a rail to be mounted with the basket to an upright pipe material of the rack, capable of smoothly pushing and drawing the basket, having saved labor, and convenient for use.

A knockdown rack, two right and left rail seats, and one basket are included. Each upright pipe material of the knockdown rack is formed into a symmetrical noncircular pipe, and horizontal through grooves are formed on both surface sides at equal distances. Projecting pieces are vertically and upwardly formed on the front and rear edges of the upper ends of two rail seats, and the projecting pieces on the front and rear ends of the rail seats are inserted in through holes in the same height of the upright pipe materials on the same side of the knockdown rack. Two rail seats are assembled onto the knockdown rack, and the basket is mounted on two right and left rails and can be feely slide.