The generation of SO2 from a refinery may affect the surrounding environment. Moreover, SO2 and its by-products are phytotoxic as berg. This study aims to investigate plant responses to SO2. The work has been designed with emphasis on using the plants directly in monitoring the contamination of the atmospheric air by SO2. An assessment was made of the impacts of long-term SO2 emissions from an oil refinery on plants located in nearby areas that are likely to be exposed to emission fallout. Three different plant species (Prosopis cineraria. Azadirachta indica, and Phoenix dactilifera) common to the environment of the Arabian Gulf were selected at different distances and directions from the refinery. The analysis of the sulphate contents of these plants were used as bioindicators for monitoring SO2 concentration levels in and around the refinery. The results of this study showed that the three different plant species responsed differently to SO2 in terms of their sulphate contents. Generally, all three species were found to be sensitive to SO2 exposure. Furthermore, the concentration of sulphate was found to be much higher closer to the refinery. On the basis of this study, it can be stated that even though SO2 levels were lower than the permissible limit values, the sulphate contents accumulated in the plants were likely to cause plant injury especially in the vicinity of the source. This suggests that the present environmental guidelines for SO2 may not protect sensitive plant species.