Reduced graphene oxide (RGO) and its composites have a great potential for their applications in optoelectronic devices. In particular, small molecules can be used for tailoring optoelectronic properties of RGO. Here, we report the fabrication of a hybrid RGO/tetrasulfonate salt of the copper phthalocyanine (RGO/TSCuPc) nanocomposite phototransistor. The device shows p-type transistor behavior in the dark which changes to ambipolar behavior at the lower light intensity, and then shows a complete n-type property at the higher light intensity. The photoresponsivity of the device can be tuned by gate voltages, and the best photoresponsivity is recorded to be as high as ∼4.6 A/W for positive gate voltage and ∼6.3 A/W with a negative sign for negative gate voltage under solar light irradiation. The observations suggest that the photogenerated free electrons of TSCuPc molecules can be injected efficiently onto RGO sheets, resulting in increases in electron conduction and hole quenching.