Article evaluated the peritoneal washings levels of a new tumor marker CA72-4 in predicting peritonealmetastasis of gastric careinoma.CA72 - 4 levels were determined in the peritoneal washings from 30 patients withgastric cancer.CA72 - 4 can significantly separate patients with over 20cm~2 serosal invasion area from those with10-20cm2area (P<0.05);CA72-4 also gave differentiation between patients with positive and negative visibleperitoneal dissemination(P<0.05); Significant difference was observ~2 peritoneal washings could be a sensitivedetector of the condition of peritoneal invasion and a new predictor of peritoneal metastasis of gastric cancer.