A modular rack comprises a plurality of upright support rods and shelves which are supported on various levels of the upright support rods in conjunction with a plurality of locating pieces, sleeves, and retaining pieces. The sleeves are fastened with the upright support rods in conjunction with the locating pieces and are provided with a retaining seat. The retaining pieces are fastened with four comers of the shelves. The shelves are releasably retained at various levels of the upright support rods such that the retaining pieces of the shelves are releasably retained by the retaining seats of the sleeves.