Molting fluid, a liquid between the old epidermis and new epidermis, plays an important role in the process of ecdysis and metamorphosis for insect. In order to explore the function of molting fluid, we used two-dimensional electrophoresis to study the molting fluid during the prepupal stage and pre-eclosion stage. More than 200 protein spots were found in the molting fluid of the 2 stages, which distributed in the 4?9 of pI and 10?180 kDa of molecular weight. We selected 42 spots to be analyzed by the matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI TOF/TOF) from the molting fluid of pre-eclosion stage, of which 34 proteins were identified successfully, including apolipoprotein, protease and protease inhibitors, chitin-binding protein and protein involved in immunity. Some of the proteins demonstrated differential expression between the two stages of metamorphosis. In order to validate the result from proteomics analysis, we studied expression of the apolipoprotein D by Q-PCR from the developmental stages. The results showed that the gene encoding apolipoprotein D had the high expression from the 1st day to the 4th day of the pupa stage, which indicated they could be involved in eclosion due to the abundant accumulation in the late pupa. Our results offered more clues for understanding the mechanism of ecdysis and metamorphosis in insect and could give reference for further study of molting fluid.