Recent advances in of silicon-based CMOS (complementary metal-oxide-semiconductor) flat panel detectors have resulted in an attractive use of cost-effective radiation imaging devices for X-ray and neutron radiography/tomography system. Indirect detection methods consisted of an X-ray converter (or a scintillator screen) and photodiode arrays are more widely used in high resolution micro-CT (computed tomography), dental and industrial NDT applications. In this study, The terbium-doped gadolinium oxysulfide (Gd(2) O(2) S:Tb, Gadox) scintillator screens with different thickness (several 30-140 mu m thickness) were directly coupled with a fiber-optic plate (FOP) of a commercially available CMOS imaging device for high resolution X-ray and thermal neutron radiography. The RadEye1 CMOS APS (active pixel sensor) imager having a large active area of 25 x 50 mm(2) and 48 mu m pixel pitch was selected for X-ray and thermal neutron imaging with high resolution. The scintillation properties and imaging performance such as relative light output, linearity and spatial resolution were measured and evaluated under X-ray and thermal neutron beam exposure. The good linearity and high spatial resolution characteristics in X-ray and thermal neutron imaging experiments were achieved by using compact, cost-effective imaging detector with exchangeable Gadox scintillator screens.