Abstract: Planting mulberry （Morus alba） not only had ecological value including windbreak and sand\|fixation， but also had a variety of economic benefits， such as increasing farmers income. With the implementing of “mulberry should be planting from southeast to northwest region”， the industry of mulberry is moving from the wet area to arid regions. The physiological mechanism of drought stress on photosystemⅡ （PSⅡ） photochemical activity have been not clear up to now， so effects of drought stress on PSⅡ photochemical activity in mulberry leaves were investigated with chlorophyll a fluorescence transient （OJIP curve） in this study. The results showed that potential photochemical efficiency of PSⅡ （Fv/Fo） and photosynthetic performance index （PIABS） based on light absorption were significantly lower than the control， which indicated that photo-activity of leaf could be inhibited by drought stress. Maximal photochemical efficiency of PSⅡ （Fv/Fm） did not have a remarkable change. The electron transmission from QA to QB in PSⅡ electronic receptor side was relatively decreased in normalized OJIP curve， and electron-accepting ability of PQ electronic library and QB were also decreased， which increased the accumulation of Q-A. Meanwhile， the activity of oxygen evolution complex （OEC） in PSⅡ electronic receptor side was inhibited， and then the photochemical activity of PSⅡ was seriously inhibited. So serious drought stress could inhibit photochemical activity of PSⅡ in mulberry， the mechanism of which might be reducing the electron transport ability in PSⅡ acceptor side and damaging the activity of OEC.

Key words: mulberry, drought stress, photosystemⅡ, chlorophyll fluorescence kinetics