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Submergence stress can greatly limit grain yield of inbred rice (Oryza sativa L.), but the effects of submergence on hybrid rice are unclear. A pot experiment was conducted to clarify the effects of submergence that happens at the vegetative growth stage on two Chinese hybrid rice cultivars. The rice cultivars Zheyou-18, an indica-japonica hybrid, and Yliangyou-689, an indica hybrid, were planted under two treatments, submergence (43 cm depth of tap water for about 2 wk) and control (no submergence). Results showed that the grain yield of submerged 'Yliangyou-689' was 539.0 g m-2 in 2018 and 614.2 g m-2 in 2019; submergence significantly reduced grain yield by 49.6% and 44.2% of that of the control. The lower level of grain yield was attributed to reduced survival rate, numbers of tillers and spikelets, plant dry weight, and crop growth rate, and excessive elongation of stems due to submergence of plants. The grain yield of submerged 'Zheyou-18' was 466.8 g m-2 in 2018 and 376.4 g m-2 in 2019 and neither of which were significantly different from that of the control, indicating higher submergence tolerance in 'Zheyou-18' than in 'Yliangyou-689'. Submergence did not affect plant N and K contents, but it reduced plant N uptake rates by 47.8% to 88.7% and it reduced K uptake rates by 53.9% to 89.5% of that of the control in these two hybrid cultivars. Furthermore, nonsignificant differences were observed in all of the parameters related to rice starch viscosity between control and submergence treatment. [ABSTRACT FROM AUTHOR]