The flexural behavior of reinforced concrete beams using recycled lightweight aggregate concrete (RLWAC) is significantly influenced by the mechanical properties of the concrete and the bond mechanism between the reinforcement and the concrete. This paper presents the results of a study on the flexural behavior of RLWAC beams using the finite element method with the Response-2000 program, accounting for material characteristics and bond stress calibrated based on experimental results. The analysis was performed on RLWAC-reinforced concrete beam models with dimensions of 150x200x2000 mm, using concrete with compressive strengths ranging from 12.5 MPa to 30.7 MPa (corresponding to concrete types C12/15 to C30/37) and CB400V reinforcing steel with diameters ranging from 10 mm to 25 mm. The research results showed that recycled lightweight aggregate concrete exhibits different stress-strain characteristics compared to conventional normal-weight concrete at the same compressive strength level, with the strain at peak stress of RLWAC being approximately 0.0028 (⁓ 0.0020 for normal-weight concrete), and the ultimate strain being approximately 0.0031 (⁓ 0.0035 for normal-weight concrete). The Response-2000 finite element software provides good predictions of the behavior of RLWAC beams, with the cracking moment and ultimate bending moment showing only small deviations from the experimental results (no more than 7%). The analysis results of the flexural behavior of reinforced concrete beams using Response-2000 show that, for the same concrete strength grade, increasing the reinforcement diameter can result in a difference in flexural capacity between RLWAC and conventional normal-weight concrete of up to 24%, and a difference in cracking moment of up to 55%. Conversely, for beams with the same reinforcement diameter, as the concrete strength class increases from C12/15 to C30/37, the differences in load-bearing capacity and crack resistance between the two types of concrete show a gradual decrease. Under load, the deflection of reinforced concrete beams using recycled aggregate concrete and conventional concrete differs by 1% to 26% at the time of crack formation and by 35%–37% when the beam reaches its ultimate moment. The largest differences occur in reinforced concrete beams with low concrete strength grades and low reinforcement ratios.