Studies showed that elevated [CO 2 ] would improve photosynthetic rates and enhance yields of rice; however, few studies have focused on the response of rice lodging, which is a major cause of cereal yield loss and quality reduction, under elevated [CO 2 ]. In this study, we examined the effects of elevated [CO 2 ] on stem and root lodging using 4 rice cultivars (86Y8, japonica hybrid; LYP9, 2-line indica hybrid; variety 9311, type of indica inbred rice, and SY63, 3-line indica hybrid) grown under two [CO 2 ] levels: 400 and 680 µmol mol -1 . Our results indicated that under elevated [CO 2 ], the stem-lodging risk (SLR) of 9311 decreased, while in SY63 the SLR increased, 86Y8 and LYP9 were not significantly affected; the risk of root lodging was reduced for all cultivars, because root biomass (instead of root number) and bending strength were increased significantly, and then the increase of anti-lodging ability is far higher than that of self-weight mass moment for all cultivars. These findings suggested that higher [CO 2 , because it directly decreases canopy photosynthesis and disturbs the translocation of C and N within shoot and root [7,8]. Setter et al.[9] demonstrated that in rice, yield losses can be as much as 1% for every 2% of stem that has lodged. Hence, if lodging risk is increased in rice under elevated [CO 2 ], the potential for increases in yield would be limited [9]. A better understanding of the mechanisms for lodging response will be helpful to reduce the incidence of lodging under elevated [CO 2 ] by enabling plant breeders to choose those characteristics in rice which are expected to increase lodging resistance, and increase food security. Lodging is accelerated by heavier panicles and longer culms, which increases the plant's mass moment (mass multiplied by distance from the point of attachment). Elevated [CO 2 ] has been shown to increase the rate of grain filling and the final weight of the panicles as a result of increased panicle size [3,4]. During the grain-filling period, panicle weight under