A curvilinear rolling guide unit allows a slider to readily straddle an endless guide rail and can prevent leakage of lubricant from a lubrication hole formed in each end cap. Each end cap is composed of an end cap body and a spacer. The end cap body has a lubrication hole, a lubrication groove, a slit which are formed in an upper portion thereof. The lubrication groove establish communication between the lubrication hole and turnaround passages. The slit extends from the lubrication hole to the under surface of the upper portion. A lubrication plug is fitted into the lubrication hole of the end cap body, closes the slit, and has a hole formed therein and serving as a lubrication passage communicating with the lubrication groove.