Flower-like bismuth sulfide (Bi₂S₃) nanostructures were synthesized from two sulfur sources, namely thiourea and thioacetamide, by microwave irradiation technique. The synthesized materials were annealed at 300 °C for 3 h. The characteristic properties of the as-prepared and annealed samples S1, AS1 (thiourea source) and S2, AS2 (thioacetamide source) were studied by XRD, SEM with EDS, XPS, UV–Vis spectra and FTIR analysis. The XRD analysis revealed that the annealing process had increased the crystallite size of the Bi₂S₃ samples. The SEM images showed that the flower-like nanostructure of both the samples (S1and S2) was changed to spherical shape (AS1) and irregular shape (AS2) respectively after annealing. The EDS and XPS results confirm the purity and the presence of the Bi and S. The UV–Vis absorption spectra revealed that the optical band gap values of Bi₂S₃ were reduced due to the annealing process. The FTIR spectra showed the functional groups present in the as-prepared and annealed Bi₂S₃ samples. The annealed Bi₂S₃ nanoparticles (AS1) showed remarkable photocatalytic activity and achieved 98.6% RhB dye degradation in 180 min. The rhodamine B (RhB) photodegradation was determined to follow a pseudo-first-order kinetic model, with a rate constant of 0.02142 min⁻¹ being the highest. After three cycles, the annealed Bi₂S₃ nano photocatalyst showed excellent reusability and stability.