Abstract:Two hybrid rice cultivars, super high-yielding Liangyoupeijiu (Pei'a i 64S×9311) and high-yielding Shanyou 63 (as control) grown in the field, wer e us ed to investigate the photosynthetic characteristics of highproduction during flag leaves development. It was shown that the contents of chl orophyll and Rubisco, the values of Fv/Fo, Fv/Fm, qP andφi in flag leaves of c v . Liangyoupeijiu were higher than those of the control, indicating that the fo rm er had greater capacity and higher efficiency for light energy absorption, transformation and utilization. The value of qN was higher and 1-qP/qN was lower in Liangyoupeijiu than in Shanyou 63, showing that the former was more tolerant to photoinhibition. Photo-carbon imbalance appeared in both cultivars during senescence of flag leaves, but which was less apparent in cv. Liangyoupeijiu. These beneficial factors in photosynthesis in cv. Liangyoupeijiu might be of importance in high production of super high-yielding rice.