This paper investigated the lateral ultimate bearing capacity of rigid pile in sloping ground. Firstly, the effective embedment depth of equivalent rigid piles of flexible piles and the mechanical characteristic of laterally loaded rigid piles are introduced. Secondly, two failure modes for the soil in front of laterally loaded piles are proposed under different directional loads at the top of piles (pointing toward and away from slope). Then, the ultimate bearing capacity of the rigid pile under different directional loads is derived on the basis of the upper limit theorem of limit-equilibrium analysis, and the rationality of the proposed method is verified by field tests. Finally, effects of the slope, internal friction angle, cohesion and load direction on the ultimate bearing capacity are investigated and some general conclusions are drawn. At the meantime, a fitting formula for the lateral ultimate bearing capacity of the rigid pile in sloping ground that considering the slope angle is proposed on the basis of the analysis results. References and guidance for design of piles in sloping ground are provided, which are valuable in both theoretical and engineering applications.