Abstract: To examine the effects of elevated CO₂ concentrations on chlorophyll fluorescence of rice leaf, a field experiment was conducted with automatic control system of CO₂ concentration in open top-chambers (OTCs). There were three treatments, including atmospheric CO₂ concentration (CK), CK+80 μmol·mol^-1 CO₂ (T₁), and CK+200 μmol·mol^-1 CO₂ (T₂). The fast chlorophyll fluorescence induction dynamic curves of flag leaves were measured using the plant efficiency analyzer at the main growth stages of rice. The results showed that T₁ treatment significantly increased quantum yield for electron transfer (φ_Eo), maximum photochemical efficiency (F_v/F_m), and performance index (PI_ABS), but decreased quantum yield for energy dissipation (φ_Do) at the flowe-ring, milk grain, ripening, and full ripeness stages. The values of φ_Eo, F_v/F_m, and PI_ABS were increased by 7.3%-23.3%, 3.1%-7.1%, and 46.2%-93.0%, respectively. The φ_Do values were decreased by 10.3%-20.5%. T₂ treatment significantly decreased φ_Eo, F_v/F_m, PI_ABS by 68.7%, 41.4%, and 93.4%, respectively, but increased φ_Do by 78.4% at the jointing stage. T₂ treatment significantly increased φ_Eo, F_v/F_m, PI_ABS by 11.6%-19.8%, 4.8%-6.8%, and 53.0%-72.6%, respectively, and decreased φ_Do by 7.7%-19.4% at the flowering, milk grain, and ripening stages. Our results suggested that elevated CO₂ concentration (80, 200 μmol·mol^-1) would promote photosynthetic electron transport of PSⅡ in flag leaves of rice.