Spinel ZnAl2O4 nanoparticles were prepared effectively by simplistic, economical microwave heating method using Hibiscus rosa-sinensis extract as reducing agent. The samples were successfully characterized by XRD pattern, EDX spectra, FT-IR analysis, HR-SEM analysis, and VSM instrumentation techniques. XRD, EDX and FT-IR results demonstrated that the products contain a pure single-phase spinel structure lacking of other secondary phase impurities. SEM results confirmed the spherical shaped nanoparticle morphology of the sample. Magnetic characterization property was confirmed by VSM analysis. VSM hysteresis loop established the superparamegnetism of the sample and the magnetization (Ms) value of ZnAl2O4 is 0.023 emu/g.