This study investigates the structural behavior of sustainable reinforced one-way lightweight self-compacting concrete (LWSCC) slabs. Six slabs were produced using three coarse aggregate types: 50% expanded perlite combined with 50% natural coarse aggregate (EPR50), 100% higher-density LECA (HD-LECA100), and 100% lower-density LECA (LD-LECA100). Natural sand was partially replaced by 25% recycled crushed brick in all mixtures, while 0.75% MSF was incorporated into three corresponding fiber reinforced mixes. The evaluated parameters included load-deflection, failure mode, secant stiffness, ductility, energy absorption, and specific load capacity were evaluated. MSF increased the ultimate load by 32.4%, 26.2%, and 22.2% for EPR50, HD-LECA100, and LD-LECA100, respectively, while stiffness increased by 31.7%, 26.4%, and 23.2%. The results demonstrate that the structural effectiveness of MSF depends on the characteristics of the lightweight aggregate (LWA) type, highlighting the importance of aggregate fiber interaction in the development of sustainable LWSCC structural members.