A study was conducted, using chlorophyll fluorescence, rapid fluorescence induction kinetics, and polyphasic fluorescence transients, to determine the effect of salt treatment and heat stress on PSII photochemistry in Rumex leaves. Salt treatment was accomplished by adding NaCl solutions of different concentrations ranging from 50 to 200 mmol/L. Heat stress was induced by exposing the plant leaves to temperatures ranging from 29 to 47 C. The control plants were grown without NaCl treatment. The data acquired in this study showed that NaCl treatment alone had no effect on the maximal photochemistry of PSII or the polyphasic rise of chlorophyll fluorescence. However, the NaCl treatment modified heat stress on PSII photochemistry in Rumex leaves, which was manifested by a lesser heat-induced decrease in photochemical quenching (qP), efficiency of excitation energy capture by open PSII reaction centers (Fv′/Fm′), and quantum yield of PSII electron transport (φPSII). The data also showed that NaCl treatment compromised the impact of heat stress on the capacity of transferring electrons from QA-to QB. Furthermore, the NaCl treatment promoted heat resistance of O2-evolving complex (OEC). In summary, NaCl treatment enhanced the thermostability of PSII.