Disclosed is a porous sepiolite having an improved water-resistance and thermal shock resistance obtained by grinding, moisture-conditioning and molding sepiolite, and then calcining said molded sepiolite at a temperature in the range of about 650.degree. C. to about 800.degree. C. Also disclosed is a porous sepiolite having a large specific surface area, wherein the pores having a pore diameter of 50 angstroms or less have a specific surface area in the range of from 40 to 200 m.sup.2 /g and in which no less than 20% of the total surface of the sepiolite is occupied with the pores having a pore diameter of 50 angstroms or less and wherein the pore distribution curve of the sepiolite has a main peak at a pore diameter of no more than 50 angstroms. This sepiolite is obtained by grinding, moisture-conditioning and molding sepiolite, calcining the same at a temperature in the range of about 650.degree. to about 800.degree. C., and then subjecting said calcined sepiolite to an acid treatment.