Abstract: Objective To identify proteins associated with growth inhibitory effects of progesterone in Ishikawa endometrial adenocarcinoma cell line (Ishikawa). Methods The total cellular proteins of the control and megestrol acetate (MA)-treated Ishikawa cells were separated by two-dimensional gel electrophoresis. After colloidal Coomassie G-250 staining and scanning, the gel images were analyzed by PDQuest software. Matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and Mascot software were used to identify the differentially expressed protein. Results and Conclusions Well-resolved and reproducible 2-dimensional patterns of both control and MA-treated Ishikawa cells were obtained. Forty-one proteins displayed differential expression after MA treatment, among which 23 were up-regulated and 18 down-regulated. Peptide mass fingerprints (PMF) by MALDI-TOF-MS analysis and search in NCBInr resulted in the identification of 8 proteins. The up-regulated proteins identified were catechol-O-methyltransferase (COMT), glutathione S-transferase, keratin 8, splicing factor 3a (subunit 3), chaperonin containing TCP1 (subunit 6A isoform a, CCT6A), RAB6A protein and AHA1. The down-regulated protein was peptidyl prolyl isomerase A (isoform 1). These findings can be helpful in further investigation of the molecular mechanism of progesterone.