Objective To explore the clinical value of expression of CEA and CK-20 detected by flow cytometry (FCM) in peritoneal washes on predicting peritoneal metastasis and prognosis of gastric carcinama.Methods Clinicopathological characteristics and follow up data of 105 patients with gastric carcinoma who were underwent D2 radical resection (R0) were collected.Peritoneal washes was collected.Peritoneal lavage cytology examination (PLC) was used to find intraperitoneal free cancer cells (IFCC).FCM was used to determine the CEA and CK-20 expressions.Meanwhile,13 patients with benign lesion on the stomach and the gastric carcinama cell line SGC-7901 were served as the negative and positive control,respectively.Results Positive expression of CEA was in 48 (45.7 ％) patients,of CK-20 was found in 67 (63.8 ％) patients,and of CEA and CK-20 was in 85 (81.0 ％) patients by FCM.However,positive expression of IFCCs was found in 31 patients(29.5 ％) by PLC.The expression of CEA and CK-20 were related to serosa invasion,lymphnode metastasis and pTNM stage (P ＜ 0.05).The median survival of patients with negative expression of both CEA and CK-20 (n =20) was significantly longer those with positive expression (n =30)(52 vs 18 months,P ＜ 0.05).Conclusions Combined Detection of CEA and CK-20 in peritoneal washes by FCM can be used to predict peritoneal micrometastasis and may predict the prognosis of gastric carcinoma.