Decidualization of human endometrial stromal (ES) cells plays a critical role in successful uterine implantation. Therefore, monitoring of the behavior of human ES cells may provide the clue for early detection of a uterine abnormality such as sterility and abortion. Monitoring of decidualization in vitro cell culture system fundamentally depends on expression of the definite biomarkers. In this study, we tried to uncover novel marker proteins of 8-bromo-cyclic adenosine monophosphate (8-Br-cAMP)-induced decidualization in human ES cells using the surface enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS). Samples were divided into three groups; control human ES cells (n=7), ES cells treated with 8-Br-cAMP (n=7) per each treatment, treated for 3,6,9, or 12 days), and cells from which 8-Br-cAMP was withdrawn for 3 days (n=7) or 6 days (n=7) after 8-Br-cAMP treatment for 6 days. Differential expressions between non-decidual control cells and 8-Br-cAMP-induced decidual cells were observed in the peaks of 9787.058 Da, 10115.45 Da, and 24031.25 Da, detected by H4 ProteinChip, and in the peaks of 10833.08 Da, 22440.88 Da, and 32777.38 Da, detected by CM10 ProteinChip. The expression patterns of these decidual markers are expected to provide invaluable information in monitoring cellular development, and further identification of these proteins may hopefully offer precious means for clinical research and therapeutic purposes.