The combination of mixed-dimensional semiconducting materials can provide additional freedom to construct integrated nanoscale electronic and optoelectronic devices with diverse functionalities. In this work, we report a high-performance dual-channel phototransistor based on one-dimensional (1D)/two-dimensional (2D) trigonal selenium (t-Se)/ReS₂ heterostructures grown by chemical vapor deposition. The injection and separation efficiency of photogenerated electron–hole pairs can be greatly improved due to the high-quality interfacial contact between t-Se nanobelts and ReS₂ films. Compared with bare ReS₂ film devices, the dual-channel phototransistor based on t-Se/ReS₂ heterostructure exhibits considerable enhancement with the responsivity (R) and detectivity (D*) up to 98 A·W^–1 and 6 × 10¹⁰ Jones at 400 nm illumination with an intensity of 1.7 mW·cm^-2, respectively. Besides, the response time can also be reduced by three times of magnitude to less than 50 ms due to the type-Ⅱ band alignment at the interface. This study opens up a promising avenue for high-performance photodetectors by constructing mixed-dimensional heterostructures.