Objectives To determine the prevalence of cancer-related anemia and iron deficiency anemia( IDA ) in patients with gastric and colorectal cancer in North of China. Methods A cross-sectional study of 262 inpatients diagnosed with gastric or colorectal cancer admitted to eight general hospitals in Beijing from August 2009 to December 2009 was performed. The blood samples were took on the day after admission and the seventh day after operation for the tests of hemoglobin, serum iron and ferritin. The morbidity of cancer-related anemia and IDA before and after the surgery was also compared respectively.Results The preoperative morbidity of cancer-related anemia was 36. 6% in 131 patients with gastric cancer, and the morbidity of IDA was 52. 1%. The mean age of the anemic patients was higher than that in cases without anemia[(62 ± 11 ) yrs vs. (57 ± 12) yrs, P ＜ 0. 05]; the postoperative morbidity of IDA increased to 72. 6% ( P ＜ 0. 05 ). In the 131 cases with colorectal cancer, the preoperative incidence of cancer-related anemia and IDA was 37. 4% and 61.2%, respectively. About 45% of the cases with anemia had a tumor in the right colon. Postoperative incidence of IDA was significantly higher than that before the surgery ( 76. 7%, P ＜ 0. 05 ). Only 10. 3% of the anemic patients were treated with chalybeate therapy before surgical procedures, and the proportion was 22. 7% after the operation. More than 50% of anemic patient received blood transfusion. Conclusions Cancer-related anemia is a common clinical manifestation in patients with gastrointestinal cancer, and anemia occurs more frequently in elder and patients with right colon tumor. The treatment to cancer-related anemia is insufficient and a systematic therapy is needed to be established.