PURPOSE: To obtain a diamond porous body useful as a chemical and heat resistant filter, a heat conductor, etc., by forming open pores between matrixes each made practically of diamond.

CONSTITUTION: A mixed layer consisting of grown diamond crystals and a non-diamond carbonaceous material is formed on a substrate such as an Si wafer. The diamond crystals have been oriented so as to make specified crystal faces parallel to the surface of the substrate. When chemical vapor growth is carried out with a gaseous methane-hydrogen mixture, the concn. of methane is regulated to 1.5-6%, preferably 3-6% and a mixed layer consisting of diamond columnar crystals oriented with the (100) faces and a non-diamond carbonaceous material is formed. The non-diamond carbonaceous material is then selectively removed by plasma etching to form pores, diamond is isostatically grown and the resulting diamond crystals are crosslinked to obtain a porous diamond body.