As a new psychoactive substance, abuse of fentanyl (FTN) is currently spreading around the world, resulting in an urgent need of on-site and rapid analytical methods for detection of FTN. Here, we present a synergistic recognition strategy for rapid, cost-effective, selective, sensitive, and visual colorimetric detection of FTN by taking advantage of Rose Bengal (RB) as the specific probe. This assay is based on the halogen- and hydrogen-bonding interactions between them, generating a charge transfer and accompanying a red shift in the RB absorption band as well as color change from red to purple. The utility of the present visual colorimetric assay is demonstrated in aqueous solution, diluted urine, and domestic sewage samples. A detection limit of 0.7 mg·L-1 in aqueous solution is achieved, and the naked-eye detection of FTN is also realized in different real matrices within 6 min. Moreover, this method is insusceptible to interference from various substances (other opioids, cutting agents of street drugs, FTN precursors, amino acids, and small-molecular amines). Additionally, we successfully fabricate a smartphone-based portable device to determine FTN, which is appropriate for field tests. The present work not only provides the first visual assay for FTN but also reveals the molecular structure-property relationship, which will guide the design and development of various probes for recognizing FTN.