A metastatic tumor model of mouse forestomach carcinoma (FC) was used in this study. Tumor cells were subcutaneously transplanted into right costal region of inbred 615-strain mice. Animals were killed on the 3rd, 6th, 9th, 12th and 15th day. Histological and haemorheological examinations were performed. Based on the histological findings the development of the tumor was divided into 5 stages; i.e. latent stage, invasive stage, early stage of metastasis, middle stage of metastasis and late stage of metastasis, corresponding with 3rd, 6th, 9th, 12th and 15th day after transplantation of mouse forestomach carcinoma. Results of haemorheological studies indicated that plasma and blood viscosity elevated in the invasion and early metastatic stages and the increased viscosity of blood was able to promote metastasis during the early stage of tumor development, while the tumor developed in the middle and late metastatic stages when the values of plasma viscosity, blood viscosity, aggregation of red blood cells and haematocrit decreased but the rigidity of red blood cells increased in these periods.