[en] Thermal conductivity of fuel compact and contact thermal conductance between fuel compact and graphite sleeve for HTGR were studied by capsule irradiation. Fuel rod of reduced size was irradiated in JRR-2, VT-1 hole in the temperature range of 700 to 1400₀C and the temperature gradient in the fuel compact and at the fuel compact-graphite sleeve interface was measured. From these values and estimated linear heat rate of fuel pin, the thermal conductivity of the fuel compact and the contact thermal conductance were calculated. In this temperature range, the thermal conductivity of the fuel compact is 0.13 to 0.18 W cm^-₁K^-₁ and the contact thermal conductance is 0.07 to 0.12 W cm^-₂K^-₁. It is found that the prediction of contact thermal conductance by the semi-experimental equation for light water reactor allows a relatively good description of that for HTGR. (author)