Pathological morphology, differentiation, cellular DNA content and cell proliferation index (PI) were comparatively studied in the primary and their corresponding metastatic lesions of 54 cases of gastric and breast cancers. The results showed that differentiation and types of metastatic cancers were in accordance with their corresponding primary cancers in more than half cases (18/34) of stomach cancers, differences could be found in the other cases (16/34), and among them, 10 were lower and 6 were higher differentially than their corresponding primary cancers. Similar results were found in breast cancer cases. Flow cytometry (FCM) analysis revealed that dramatic DNA Index (DI) differences between metastatic and their corresponding primary cancers existed in 6/34 of gastric and 4/18 of mammary cancers, among them 7 cases were higher than the primary while 3 were lower than the primary (DI) . Similar results could also be found in PI analysis. All these suggested that metastasis of gastric and breast cancer was a very complicated process and metastatic cancer did not necessarily always show lower differentiation, higher DNA contents and DNA aneuploidy as well as higher cell proliferative rate.