PURPOSE: To produce the title foam having large open-cell volume, by molding carbonaceous microballoons together with a binder, pressurizing the product to rupture part of the microballoons in the product while retaining the spherical shape thereof and carbonizing the product.

CONSTITUTION: Carbonaceous microballoons 7 having a particle size of 200W2,000μm are mixed with a powdered inorg. or org. binder 3 having a particle size of not larger than 250μm (e.g., a phenolic resin) in such a manner that the microballoons 7 are not ruptured. The mixture is put into a heated vessel and pressure-molded to obtain a preform 6 for carbon foam, in which voids 4 are formed among the binders 3 and the microballoons 7 having neither crack nor rupture. The preform 6 is optionally cured and pressurized under a pressure which is not higher than the compression strength of the preform 6 to rupture part of the microballoons while retaining the spherical shape thereof. The preform 6 is carbonized by heating it in vacuo or in a non-oxidizing gas to obtain a carbon foam 1 wherein the voids 4 are formed among the binders 3 and the microballoons 7 having the rupture 5 while retaining the spherical shape thereof.