Black phosphorus nanosheets (BP NSs)-decorated single-layer WS2 phototransistors were fabricated by drop-casting the liquid-phase exfoliated BP NSs atop the channel of single-layer WS2 grown by chemical vapor deposition technique. It was found that, upon the decoration of BP NSs, the BP/WS2 hybrid phototransistor exhibited an enhancement of responsivity and extension of response spectral range. The responsivity is up to 120 mA/W in the hybrid phototransistor, being about 20 times larger than that in devices based on the pristine single-layer WS2. Moreover, the hybrid device possess high response speed with the response and recovery time of similar to 54 and similar to 140 mu s, respectively, and also excellent photoswitching stability.