Acesulfame potassium (AK) is widely used in the food industry. However, it does harm to the liver and nervous system. Here, a rapid method based on surface-enhanced Raman spectroscopy (SERS) was developed for the detection of AK in mouthwash. As the results show that the characteristic peaks of AK were at 549, 641, and 1650 cm − 1. The vibrational modes of each peak were calculated by density functional theory. This method can detect AK in mouthwash samples within 3 min without any complicated pretreatment. These results suggested that this SERS-based method for rapid determination of AK in mouthwash was sensitive and reliable. It is expected that this method possesses great potential in monitoring the quality of mouthwash.