The changes of sorbitol content, sorbitol dehydrogenase (SDH) activity and protein expression in bagging ‘Red Fuji’ apple fruit were studied through enzyme determination and Western blotting technique. The results showed that the sorbitol content and SDH activity in bagging ‘Red Fuji’ apple fruit almost had the same dynamic changes as control fruit during the whole developing period. Moreover, the relative lower SDH activity and higher sorbitol content were found in bagging apple fruit compared with control. Therefore, fruit bagging influenced sorbitol metabolism in some extent. On the other hand, Western blotting assay of SDH detected the presence of 40 kDa peptide and the intensity of immune signal in apple fruit increased gradually with fruit developing. However, few significant differences of immune signal existed in bagging and control fruit at the same sampling period. So it was concluded that the changes of SDH activity was regulated at post-translational level.