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We describe our studies of the influence of Cr content in an Al₂O₃-Cr composite on its thermal and electrical conductivity properties during and after electron-beam sintering in the forevacuum range of pressure. Sintering was carried out using a plasma-cathode forevacuum-pressure electron source of an original design, capable of processing non-conducting materials directly. It is shown that the chromium content affects the efficiency of the beam power transfer to the irradiated composite. The efficiency decreases with increasing chromium content. Measurement of the composite’s coefficient of thermal conductivity, in the temperature range 50–400 °C, shows that it varies almost linearly from 25 W/(m∙K) to 68 W/(m∙K) as the Cr content in the composite increases from 25% to 75% wt. The electrical conductivity properties after sintering exhibit a non-linear behavior. The conduction activation energy E_a, measured via the dependence of the current through composites of different compositions, is slightly lower than the Al₂O₃ band-gap. The addition of metallic Cr results in a disproportionate decrease in E_a, almost by an order of magnitude, from 6.9 eV to 0.68 eV. By varying the chromium content, it is possible to form a material with thermal and electrical conductivities controllable over a wide range.