The aim of the present study is to find a simple and convenient method of measuring the density of the porous carbonaceous substances. From the reexamination of the usual picnometer method several improvements were introduced. First butanol is recommended as an immersion medium in place of benzene. Second a piconometer which is convenient to treat carbonaceous powders was newly designed. It has proved that the scheme described in this paper gives satisfactory results from the viewpoint of the industrial testing.