Temperature-dependent in-situ Raman spectroscopy is used to investigate the phase transformation of zinc metastannate (ZnSnO3) to zinc orthostannate (Zn2SnO4) induced upon annealing in the ambient. ZnSnO3 microcubes (MCs) were synthesized at room temperature using a simple aqueous synthesis process, followed by characterization using electron microscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). Annealing of the ZnSnO3 MCs was carried out up to 1000 degrees C, while recording the Raman spectra in-situ at regular intervals. Phase transformation from metastannate to orthostannate was found to begin around 500 degrees C with an activation energy of similar to 0.965 eV followed by the recrystallization into the inverse spinel orthostannate phase at similar to 750 degrees C. Results from this study provide detailed understanding of the phase transformation behavior of perovskite ZnSnO3 to inverse spinel Zn2SnO4 upon thermal annealing.