Present study reports the hydrothermal synthesis procedure to prepare the facile and sustainable orthorhombic Molybdenum trioxide (α-MoO3) nanoparticles (NPs) for the degradation of thymol blue dye. Synthesized α-MoO3NPs was characterized by FTIR, XRD, Zeta-potential, SEM, and TEM to investigate the functionalities, texture, size, and morphology of α-MoO3 NPs. The average size was calculated up to 68 ± 5 nm. The α-MoO3NPs was successfully applied to degrade toxic organic dye (thymol blue) in aqueous media. To achieve maximum percentage degredation of dye different parameters were optimized, including a catalyst dose, reaction time, effect of microwave irradiation at low power, reproducibility of catalyst. At optimum conditions, the fabricated α-MoO3NPs-based heterogeneous nano-catalyst was highly efficient for degrading thymol blue dye in aqueous media; the percentage degradation was obtained up to 99% within 60 s just using 120 µg of α-MoO3NPs was used under the microwave radiations. The heterogeneous nano-catalyst shows excellent performance and is highly efficient as compared to previously reported work. The schematic diagram for the degradation of thymol blue dye using prepared MoO3 nano-catalyst [ABSTRACT FROM AUTHOR]