This paper presents the results of both theoretical and experimental studies on the influence of bond stress on the formation and development of cracks in reinforced concrete beams made with 100% recycled lightweight aggregates. Experimental studies to determine the parameters of concrete using recycled lightweight aggregate (RLWA) were carried out on three mix designs, M1, M2, and M3, with corresponding compressive strengths of 15 MPa, 25 MPa, and 35 MPa, respectively. The experiments to determine the bond-slip relationship between recycled lightweight aggregate concrete and reinforcing steel were conducted on cubic specimens with dimensions of 150 x 150 x 150 mm and reinforcing bars with a diameter of d = 12 mm The tests investigating the cracking behavior of reinforced beams made of recycled lightweight aggregate concrete (RLWAC) under flexural loading were carried out on beam specimens under four – point loading with simply supported supports. The cracking moment, the cracking width at steel yield, and the cracking width at the maximum moment of the beams were compared with the provisions of TCVN 5574-2018 and Eurocode 2 and the proposed theoretical method. The research results indicate that the bond strength between reinforcing steel and recycled lightweight aggregate concrete is lower than that of conventional concrete. This is mainly attributed to the weak interfacial transition zone (ITZ), the porous nature, and the high water absorption of the recycled lightweight aggregates. The results from tests on reinforced concrete beams under flexure showed that RLWAC beams exhibited earlier crack initiation, faster crack propagation, and larger crack widths than conventional reinforced concrete beams. The analytical results based on the proposed theoretical model for calculating the cracking moment and crack width of reinforced concrete beams using RLWAC are closer to the experimental results (with errors of 2–7% for cracking moment and 19–23% for crack width) than those obtained according to TCVN 5574:2018 and Eurocode 2. These results contribute to establishing a scientific basis for the design and crack control of reinforced concrete members using RLWAC.