Abstract: Bagging is an effective method of improving fruit quality in fruit production and has been widely used to improve fruit appearance，decrease pesticide/fungicides residues and increase commercial value. In order to compare the effects of different bag materials on internal fruit quality，the effects of purple plastic film bag and single-layer white paper bag（Kobayashi NK-15）on soluble sugars，organic acids，and aroma compounds in Pyrus sinkiangensis Yü‘Korla Xiangli’fruit were investigated by high performance liquid chromatography（HPLC），headspace solid-phase microextraction（HS–SPME）combined with gas chromatography-mass spectrometry（GC–MS）with non-bagged fruit as control. The results showed：(1) There were no significant differences in sugars contents between fruit with purple plastic film bag and non-bagged fruit. The contents of sucrose and sorbitol in fruits with single-layer white paper bag were significantly lower than that of non-bagged fruit（P < 0.05）but there were no significant differences in the contents of glucose and fructose. (2) Compared with non-bagged fruit，the content of malic acid were reduced significantly（P < 0.05）in fruit with purple plastic film bag and the contents of citric acid in fruit with single-layer white paper bag were increased significantly（P < 0.05）. However，there were no significant differences in the contents of shikimmi acid，oxalic acid and quinic acid among different treatments. (3) There were distinct differences in the composition and contents of volatile compounds among different treatments. Bagging reduced volatiles varieties and relative contents of pear fruit，especially for esters with fruity smell. These results potentially suggest that bagging limite formation of whole fruit flavor，but the negative effects of plastic film bag on fruit flavor compounds lower than paper bag，and therefore the plastic film bag should be selected firstly in bagging cultivation of‘Korla Xiangli’fruit together with cost and work efficiency.

Key words: pear, bagging, soluble sugar, organic acid, aroma