Abstract: The change of catalase activity in 12 tobacco cultivars with different resistances after inoculating cucumber mosaic virus and its relationship with tobacco resistance were studied.The results showed that the catalase activity in resistant or susceptible cultivars was lower than that of the control;however, there was no significant correlation between the change of catalase activity and the resistance of tobacco cultivar.Analyzing with Data Progress System, indicated that there was no significant correlation between the change of catalase activity or its average value and disease index.It is not feasible to use the change of catalase activity before and after inoculation as an indication of plant resistance in tobacco-CMV interaction system.