Microwave freeze drying (MFD) normally contains three stages, i.e., pre-freeze stage, primary drying stage and secondary drying stage, just as in conventional freeze drying. This research examines the variations of structure, starch content, reducing sugar content, color change as well as expansion ratio during these stages of microwave freeze drying banana chips. Results show that biggest changes are found at the primary drying stage in the banana slices' starch content, reduced sugar content, their structure and their changed colors while the biggest change of expansion ratio occurs at the secondary drying stage. Similar results can also be obtained for FD samples. Thus it is concluded that the primary stage can do most damage to the banana chips. (C) 2010 Published by Elsevier Ltd.