Single-crystalline nano/microwires (NWs/MWs) based on organic semiconductors have attracted great interest recently as they are promising building blocks for optoelectronic applications. The development of organic phototransistors (OPTs) based on n-channel NWs/MWs is highly desirable for the bottom-up fabrication of photoelectronic circuits, which provides high operational stability, easy control of photoswitching voltages, high photosensitivity and responsivity. To date, however, single-crystalline NWs/MWs OPTs have been far less employed. Herein, we report organic single-crystalline NW-OPTs fabricated using a high-performance n-channel organic semiconductor, N,N'-bis(2-phenethyl)-perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI), mainly focusing on the photoelectronic characteristics. Highly sensitive and reproducible photo-responses compared with vacuum-deposited thin-film devices were observed from the NWs/MWs OPTs and photogenerated charge carrier behaviors were quantitatively investigated.