The present study aimed to investigate the sensitivity of an indigenous leguminous plant species of Oman, Prosopis cineraria (ghaff tree), to SO2 pollutant. Plants were exposed to 0, 25, 50, 100 and 150 ppb SO2 for 30 min daily for the period of ten weeks, under light and dark conditions. The formation of marginal necrotic areas on leaflets was seen as the first symptom of SO2 injury in P. cineraria plants. Leaf senescence was highly significant (p<0.01) in plants exposed to SO2 in light conditions and significant (p<0.05) in plants exposed to SO2 in dark conditions compared with control plants. There was significant (p<0.05) decrease in Relative Growth Rate per week in plants exposed to SO2 in both light and dark treatments compared with control plants, but more pronounced reduction in light conditions. Stomatal conductance was significantly (p<0.01) reduced after SO2 exposure in both light and dark treatments. These results became the first record of Oman indigenous plant species showing confirmed injuries as a result of exposure of SO2 concentrations.