This paper proposes a method for the nonlinear analysis of laterally loaded single reinforced concrete piles based on the beam-on-nonlinear-Winkler-foundation approach. A nonlinear fiber beam-column element is used to model the nonlinear behavior of a pile. The pile is divided into a series of segments, of which the cross section is assumed to be plane and normal to the longitudinal axis. The internal force of a segment is derived by integrating the nonlinear stress-strain relationships of all steel and concrete fibers within the cross section of the segment. The substructure technique is introduced to calculate the stiffness matrix of the segments. The nonlinear behavior of soils surrounding the pile is characterized by a modified strain wedge model. The results show that (1) the predicted results using the proposed method are consistent with the measurements for all three full-scale tested piles, and (2) updating the neutral axis of segments has a significant effect on the calculated lateral deflection; however, it has a slight effect on the calculated bending moment. Moreover, an empirical equation is derived from the numerical analyses for estimating the cracked flexural rigidity of bored piles subjected to lateral loading.