The flexural behavior of reinforced foamed slag lightweight concrete (FSLWA) beams was investigated by altering two main parameters in two phases. Phase 1, the proportion of normal-weight aggregate (NWA) that lightweight aggregate (LWA) replaces varied in five beams. The proportion of replacement (0%,25 %, 50%, 75%, and 100 %). In phase 2, five beams were used with the variable depths of lightweight aggregate concrete (LWAC) in the tensile zone, including the normal-weight concrete (NWC) as a control specimen. Lightweight aggregate concrete depths are equal to (25%, 50%, 75%, and 100%) of the beam's overall depth, as determined from the bottom surface. The Lightweight concrete (LWC) used in the study was produced with volcanic tuff as a lightweight aggregate. A two-point loading test was performed on each beam and were gradually loaded until failure. The central deflection of the beams was measured at each load increment. Additionally, the beginning of cracks and the failure mode was observed. The findings indicated that the maximum compressive strength of the Lightweight aggregate concrete was comparable to that of the control specimen. No shear failures were observed in the tested beams, and the bond between the Lightweight aggregate concrete and normal weight aggregate concrete (NWAC) layers was determined to be strong. The specimens with 25% volcanic tuff in phase 2 had the best results, which had a strength of 41.88 MPa and a density of 2170 kg/m3, similar to those of normal-weight concrete (NWC). However, the stiffness of these specimens was 24% lower than that of normal-weight concrete. Results suggest that producing lightweight concrete beams using volcanic tuff as a lightweight aggregate may be a viable option for certain applications. However, the use of volcanic tuff as a lightweight aggregate may also involve certain trade-offs in terms of workability and stiffness that should be carefully considered.