A semiempirical method for the determination of mass absorption coefficients for the very soft x‐ray region of 5 to 50 A is described. A universal function for the absorption byK‐shell electrons and another for absorption byLand extra‐Lshell electrons are given in table form to permit the calculation of mass absorption coefficients for elements of atomic number up to 36. Calculated and observed values from available absorption data are compared with those predicted by quantum theory. Tables are given for the mass absorption coefficients for nine useful wavelengths in the ultra‐soft region, 8.34, 13.3, 17.6, 21.7, 23.7, 27.4, 31.6, 36.3, and 44 A.