A ball circulation system for linear guide way includes a slide rail, a slider coupled with the slide rail, and two end covers of the slider with an oil scraper. A cross-wise circulation passage and a separated circulation passage respectively formed at two side of the end cover are integrally combined in one structure so as to form two independent and opposite ball circulations. By so space in the circulation system is able to accommodate more rolling balls by twice filling procedure thereby improving the efficiency of assembly work. Besides, up and down motion of the rolling balls during circulation causes a uniform lubrication effect. Allowing accommodation of more rolling balls means substantially improving load carrying ability of the linear guide way.