Photoconductive properties of the a-Si:H/ a-C:H structure formed by the rf glow discharge process were evaluated from 1-V characteristics and the photocurrent spectra in visible light.The optical energy gaps of the a-Si:H layer and the a-C:H layer were 1.7 and 2.8 eY, respectively. The photocurrent was dominated by carriers generated in the a-Si:H layer, and the carriers were injected from the a-Si:H layer to the a-C:H layer. The dark current flowing in the a-Si:H/ a-C:H structure depended on both the thickness of the a-C:H and the polarity of the bias voltage. At the bias voltage of 2 Y, the photosensitivity of the a-Si:H (320 nm)/a-C:H (5 nm) heterostructure, which was defined as the ratio of the photocurrent to the dark current, was larger than that of the a-Si:H film by three orders of magnitude.