This study reports the first polymer vesicle sensor for the visual detection of SO2 and its derivatives in water. A strong binding ability between tertiary alkanolamines and SO2 has been used as the driving force for the detection by the graft of tertiary amine alcohol (TAA) groups onto an amphiphilic hyperbranched multiarm polymer, which can self-assemble into vesicles with enriched TAA groups on the surface. The polymer vesicles will undergo proton exchange with cresol red (CR) to produce CR-immobilized vesicles (CR@vesicles). Subsequently, through competitive binding with the TAA groups between CR and SO2 or HSO3-, the CR@vesicles (purple) can quickly change into SO2@vesicles (colorless) with the release of protonated CR (yellow). Such a fast purple to yellow transition in the solution allows the visual detection of SO2 or its derivatives in water by the naked eye. A visual test paper for SO2 gas has also been demonstrated by the adsorption of CR@vesicles onto paper. Meanwhile, the detection limit of CR@vesicles for HSO3- is approximately 25 nM, which is improved by approximately 30 times when compared with that of small molecule-based sensors with a similar structure (0.83 μM). Such an enhanced detection sensitivity should be related to the enrichment of TAA groups as well as the CR in CR@vesicles. In addition, the CR@vesicle sensors also show selectivity and specificity for the detection of SO2 or HSO3- among anions such as F-, Br-, Cl-, SO42-, NO2-, C2O42-, S2O32-, SCN-, AcO-, SO32-, S2-, and HCO3-.