A retainer is used for a linear guideway, including a main body, a retaining portion, and a hollow portion. The main body extends along the longitudinal direction of the retainer. The retaining portion extends from a long side of the main body along the width direction of the retaining portion. The hollow portion is abutted between the retaining portion and the main body for allowing a part of the retaining portion to be elastically deformed when the retaining portion is compressed by an external force. Therefore, when balls are assembled, the retainer of the present invention uses the partial elastic deformation of the retaining portion to avoid damage caused by directly collided with the balls, thereby enhancing convenience of installing and removing the balls. In addition, the hollow portion can be used to save lubricating oil for achieving the effect of extended lubrication.