The electrical resistivity of carbon blacks was measured under compression (up to 9 kilobars) at room temperature using a pressure vessel of the piston-cylinder type. The slope of the logρ vs. logP relation was about −0.5 for all the carbon black specimens except the original channel black. For the thermal blacks heat-treated above 2100°C, i. e., the graphitized thermal blacks, the linear relation between logarithms of resistivity, ρ, and of pressure, P, broke at about 2.5—4.5 kilobars. After the break the slope of the logρ vs. logP relation for the graphitized thermal blacks had the same value as that for natural graphite. The original channel black had a value of the slope as high as −0.9, but the 1300°C-treated channel black had a value similar to that of the other samples. This was probably due to the removal of the high-resistance film on the particle surface by the heat treatment. The first stage of the decrease in electrical resistivity with an increase in the pressure seems to be due to the yieldi...