This study investigated the behavior of a non-corroded reinforced concrete (RC) beam and two RC beams with non-uniform corrosion (whole span and side span) in a four-point bending test. The corrosion distributions of the tensile steel rebars were measured by two methods: diameter loss and mass loss. The peak values of corrosion distribution in the diameter-loss measurements were much greater than those in the mass-loss measurements. However, the average corrosion according to the diameter measurements was smaller than that in the mass-loss measurements. The corrosion distribution trends were the same in the two methods, indicating good measurement accuracy. From the bending test results, it appears that increasing corrosion area and corrosion ratios reduce the beams’ stiffness, yielding capacity, and ultimate capacity. All three specimens had similar failure patterns: steel yielding followed by compression failure of the concrete. A nonlinear three-dimensional (3D) analysis model that considered the non-uniform corrosion of the rebars was established and verified by experimental data. The model’s predictions for stiffness, ultimate capacity, and failure patterns were consistent with experimental results. The spatial variability factor (R'), which is the ratio of the maximum corrosion ratio (γ_max) to the average corrosion ratio (γ_ave), was adopted to quantify the non-uniformity of the corrosion distribution in this study.