The effects of 0.5 and 1.0 ppm of ozone on the developing chloroplast of barley (Hordeum vulgare L) seedling during greening were investigated by PSI and II activities, chlorophyll fluorescence, and the contents of chlorophyll. Etiolated barley seedling was treated 0.5 and 1.0 ppm ozone for the first 4 h during greening. In 24 h greening experiment, the contents of chlorophyll were decreased by increasing ozone concentration from 0.5 ppm to 1.0 ppm. In 24 h greening experiment, Fo, Fv, Fm and qE were greatly decreased as the concentration of ozone was increased, but those were not considerably decreased in 48 h greening experiment. In another experiment, the developing barley seedling was treated with 0.5 and 1.0 ppm ozone for the last 4 h during greening period, which was 24 h or 48 h. In both experiments the PS II activity was decreased as the concentration of ozone was increased, but not in PS I activity. Fv, Fm and Fv/Fo were also decreased as the concentration of ozone was increased. qP and qR were strikingly decreased as the concentration of ozone was increased in both experiments.iments.