The graphite diffusion length was measured as a function of temperature in a 101-inch cube of graphite. A water-cooled BF3 counter was used as the neutron flux detector, with additional measurements being made with gold and indium foils. The steady state neutron flux was furnished by means of four -gram, Ra-Be neutron sources. Measurements were taken over a range of temperature from 22°C to 600°C at intervals of about 50°C. The variation of diffusion length with temperature change is in good agreement with the calculated variation assuming a 1/υ cross section for graphite and a constant transport mean free path.