Abstract: Objective To study the total length, total volume, total surface area and average diameter of the capillaries in rat white matter and cortex. Methods In the present study, 5 adult LongEvans rats (7 months) were used. The length density, volume density, surface area density and total length, total volume, total surface area, average diameter of the capillaries in white matter and cortex were estimated with the stereological techniques and immunohistochemistry technique. Results The tissue processing induced volume shrinkage of rat white matter (±s) was 0.51 ± 0.09. The total length, total volume, total surface area and average diameter of the capillaries in the white matter was (30.9 ± 6.2) m，(0.8±0.09) mmSUP>3/SUP>，(5.3±0.74)cmSUP>2/SUP>，(5.5±1.1)μm. The tissue processing induced volume shrinkage of rat cortex was 0.57±0.08. The total length, total volume, total surface area and average diameter of the capillaries in the cortex was (364.8±68.0)m，(7.0±1.6)mmSUP>3/SUP>，(51.6±11.

Key words: Cortex, White matter, Capillary, Immunohistochemistry, Stereology, Rat