Abstract: The study was conducted to investigate physiological reactions of photosystem Ⅱ in leaves of mulberry to NaCl and Na2CO3 stress using the fast fluorescence transients as technology. The results showed that fluorescence parameters had no difference under low concentration NaCl (100 mmol/L) treatment, but the fluorescence parameters of normalised total complementary area above the OJIP transie (Sm), quantum yield for electron transport (φE0), maximal trapped energy flux per reaction center (TR0/RC) and electron transport flux per reaction center (ET0/RC) decreased obviously when NaCl concentration was above 100 mmol/L, while the parameters of relative variable fluorescence intensity at the Jstep (VJ), the reduction of QA maximum rate (M0), quantum yield for dissipated energy (φD0) and dissipated energy flux per reaction center (DI0/RC) increased. Electron transports in the receptor side of PSⅡfrom QA to QB were impeded under salt stress, the main reason was that the locus of QB and capacity of PQ had been changed, the ratio of capture photons had been decreased, the ratio of heat energy had been increased, the electron had been reduced after QA. The PSⅡphotochemical efficiency (Fv/Fm) and PSⅡ potential activities (Fv/F0) in mulberry leaves under 200 mmol/L NaCl stress had been significantly increased, and photoinhibitation was occurred. Meanwhile, high pH in alkali salt (Na2CO3) decreased pH difference between inner and outside thylakoid membrane at the same Na+concentration as neutral salt to inhibit or injure PSⅡ. It is concluded that PSⅡin mulberry leaves is damaged heavier under alkali salt stress than that of neutral salt (NaCl).