In order to investigate the effects of exogenous trehalose on gene expression of Rubisco and Rubisco activase (RCA) in wheat under osmotic stress, we used the droughtresistant variety ‘Jinmai 47’ and the droughtsensitive variety ‘Zhengyin 1’ as materials. The results showed that：（1） exogenous trehalose and osmotic stress both could increase the content of trehalose in wheat leaves. （2） Osmotic stress significantly reduced the net photosynthetic rate of wheat leaves, while exogenous trehalose could obviously relieve the decline of the net photosynthetic rate. （3） Relative expression and protein content of Rubisco large subunits (rbcL) were dramatically decreased under osmotic stress in ‘Zhengyin 1’. In addition, osmotic stress observably decreased the relative expression of RCA α and β subunits, as well as the protein content of RCA. However, exogenous trehalose could not alleviate the decline of RCA protein content. Osmotic stress notably reduced Rubisco total activity, initial activity, activation status and RCA activity of. Nevertheless exogenous trehalose could prominently alleviate these indexes. （4）The relevant analysis indicated that the net photosynthesis rate was significantly positively correlated with the relative expression of rbcL, RCA α and β subunits, Rubisco total activity, initial activity, activation status and RCA activity. In conclusion, exogenous application of trehalose plays a substantially protective role in Rubisco and RCA activity from posttranslational level under osmotic stress, thereby alleviating the decrease of photosynthetic rate.