$ZnGa_2O_4$ thin film phosphors have been deposited using a pulsed laser deposition method on Si(100) substrates at a substrate temperature of $550^{circ}C$ with oxygen pressures of 100mTorr, and subsequently to investigate their photoluminescence characteristics after post-annealed at $600^{circ}C$ and $700^{circ}C$. As a result for X-ray diffraction, $Ga_2O_3$ shape appeared with increasing annealing temperature. The luminescent spectra show a broad band extending from 350 to 600nm peaking at 460nm. A post-annealing treatment of $ZnGa_2O_4$ thin films led to the different shape of luminescent intensity and grain size.