High quality In-doped ZnO single crystal was grown using the hydrothermal method. The growth rate for both <0001> and <000-1> directions is about 80 m/day. The X-ray rocking curve (XRC) full width at half maximum (FWHM) of the (0002) reflection is 24.2 arcsec. In order to make it possible to use this material as a scintillator for in situ imaging of soft X-ray laser with high spatial resolution, we prepared an In-doped ZnO wafer (9.0 mm x 9.0 mm x 0.75 mm) and mounted it on a vacuum flange. The decay time constant is evaluated to be 120 ps, therefore making it an ideal scintillator for in situ imaging device of soft X-ray laser with high spatial resolution. Furthermore, In-doped ZnO scintillator with such short decay time constant is suitable for high accuracy alignment and synchronization of ultrafast, short wavelength laser sources for pump-and-probe experiments.