With Japonica rice BRS Firmeza and indica rice BRS Pelota (low and high grain yield, respectively) as materials, Chl content and Chl a fluorescence parameters in flag leaves from the heading to mature grain stage were investigated. The Chl content and the Chl a fluorescence were measured using a portable chlorophyll meter CL-01 and portables fluorometer Handy-PEA and FMS-2 (Hansatech, Kings Lynn, UK), respectively. All measurements were taken on middle part of the flag leaves (n = 10). The results showed that the Chl content and Chl a fluorescence parameters declined after full expansion of flag leaves in both rice cultivars. However, these biochemical and photochemical parameters did not show similar changing pattern and the behavior of flag leaves senescence showed some differences between BRS Pelota and BRS Firmeza rice cultivars. During the senescence of flag leaves, BRS Pelota, the rice cultivar with higher grain yield capacity, was characterized by significant reductions in Chl content, PI ABS,Total , TR 0 /ABS, ET 0 /ABS, ET 0 /TR 0 , RC/ABS compared to BRS Firmeza. On the other hand, DI 0 /RC, TR 0 /RC and ET 0 /RC were significantly higher in BRS Pelota. These results show that the decreased photosystem II activity, evaluated through chlorophyll fluorescence analysis, was resultant of leaves senescence process, which was much more expressive in BRS Pelota rice variety. We suggest that the higher productivity of BRS Pelota rice cultivar results from its higher assimilate mobilization ability or energy usage efficiency, in despite of its lower light absorption capacity. quenching, φ PSII , actual PSII efficiency; PI ABS,Total , total performance index, measuring the performance up to the PSI end electron acceptors; PSI, photosystem I; PSII, photosystem II; Q A , electron acceptor of PSII; qP, photochemical quenching coefficient; RC/ ABS, ratio of reaction centers and the absorbance; RE 0 /TR 0 = δ R0 , efficiency with which an electron can move from the reduced intersystem electron acceptors to the PSI end electron acceptors; TR, trapping of excitation energy; TR 0 /RC, trapped energy flux per RC; φ PSII , actual PSII efficiency; φ Do quantum yield of dissipation; φ Ro , quantum yield for the reduction of end acceptors of PSI per photon absorbed; RE 0 /TR 0 = ρ 0 , efficiency which a trapped exciton can move an electron into the electron transport chain from Q A  to the end electron acceptors of PSI; Ψ 0 = ET 0 /TR 0 , yield of electron transport per trapped exciton.