Two-dimensional a-Si photodiode arrays with the a-Si TFT readout scheme were fabricated. Some performance characteristics were investigated for detecting visible light, X-ray and γ ray. Arrays of 64×40 1mm2-pixels have good uniformity with ± 1 % in linearity variation, ± 10 % dark current variation and ± 5 % sensitivity variation. The cross-talk between adjacent pixels was found to be negligible so that the intrinsic spatial resolution was determined entirely by the pixel size. Due to the high resistivity of a-Si photodiodes and TFTs, charges generated by pulsed light illumination were retained in photodiodes for a long period of time. This enables the accumulation-mode operation for detecting low-intensity light, where only one image is obtained over a long integration time. An encapsulated Co-57 source (3 μ.Ci) was successfully imaged with 5 sec integration. Alternatively, the array can be operated by the cine-mode for detecting high-intensity light, where a number of images are obtained successively.