A circulating system for a linear guideway comprises a slide block, a slide rail, two cover plates, two end caps and plural rolling elements. The slide block is disposed on the slide rail. The two cover plates and the two end caps are disposed at two opposite ends of the slide block, respectively. Between the two cover plates and the two end caps are disposed inner return and outer return blocks, respectively, and the inner return and the outer return blocks each are defined with half rolling paths to form complete rolling paths. Both ends of a complete rolling path and both ends of a complete loaded path are connected to both ends of two complete return paths to complete circulation paths. The inner and outer return blocks are made by common plastic injection molding, and the formed rolling paths are made of plastic material.