Clonal integration, allowing resource to be shared between ramets, is a unique biological characteristic for clonal plants. Ramets of stoloniferous and rhizomatous species internally translocate resources from sites of high supply to sites of high demand via physical connections among them, resulting in enhanced performance of ramets and/or ramet system under environmental stresses. On the other hand, environmental stresses always induce accumulation of reactive oxygen species (ROS), which attack membrane integration, deactivate protein function and subsequently interrupt normal metabolism process. Although there is a large body of knowledge on how clonal integration improves the performance of clonal plants, its effect on the activity of enzymes responsible for scavenging ROS, remains unknown. Here we investigated the influence of clonal integration on ROS of Cynodon dactylon,a stoloniferous clonal herb commonly found in riparian areas of reservoirs, subjected to waterlogging stress. Clonal fragments with 4 ramets were placed in pots divided into 2 chambers. The 2 apical (relatively younger) ramets of each fragment were submerged in water at depth of 0(control) or 15 cm, with the stolons connecting to the basal (relatively older) ramets under normal condition either severed (preventing clonal integration) or not (allowing integration). The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) from root tissue of apical and basal ramets of C. dactylon were measured. Meanwhile, the biomass of apical and basal ramets after 20 days' treatments was also measured to investigate whether clonal integration executed "enhancing effect" on performance of C. dactylon. Compared to 41.4% reduction of apical biomass under connection and waterlogging treatment, severing significantly decreased apical biomass by 58.8% under waterlogging stress, suggesting that clonal integration could improved the performance of apical ramets of C. dactylon. However, such effect was not found in terms of basal biomass. Under waterlogging stress, physical connection greatly increased root SOD activity of apical ramets up to control level, while disconnection significantly decreased it to 41.7% of the value of the control treatment. Furthermore, disconnection combined with waterlogging treatment also drops root APX and CAT activity of apical ramets to some extents. On the other hand for basal ramets, physical connection induced significant reduction of root SOD and CAT activities to 35.8% and 51.3% of the control level under waterlogging stress. These results illuminated that clonal integration could ameliorate the balance between regeneration and scavenging of reactive oxygen species under waterlogging stress imposed to apical ramets, which probably was one of the key biochemical processes responsible for the enhanced performance of clone plants. To our knowledge, this is the first report that clonal integration affects the activities of SOD, APX, and CAT, the three key enzymes responsible for scavenging reactive oxygen species which would commonly accumulate and subsequently interrupt plants' normal metabolism under environmental stresses. Therefore, we suggested that clonal integration could not only adjust anatomic/structural/physiological processes, but also ameliorate the balance between regeneration and scavenging of reactive oxygen species, to improve the performance of stressed ramets. Furthermore, we also thought that resource transport between apical and basal ramets was the main mechanism attributed to the variation of ROS scavenging enzyme activity.