A novel ex vivo method to determine the cell adhesion of cancer cells to the peritoneum was described. The wells of a microtiter plate were filled with cell suspension and sealed using mouse peritoneum. The peritoneum was fixed using a plastic cover and the plate was turned upside down and incubated for cell adhesion. After incubation for 80 min, the plate was centrifuged and non-adherent cells were assayed by MTT assay. Human cancer cells (MKN28, MKN45, MKN74, KM12C and KM12SM) adhered to the mouse peritoneum as well as cells from mouse (Colon26) and the ratio of cells attached to the peritoneum was estimated to be between 12.8 and 66.4%. This simple method could be useful to investigate the adhesion molecule associated with peritoneal dissemination.