Abstract: A new equation for calculating the heat of vaporization was derived For alkanes, monoolefines, ethers (nonring) , nitrils, ketones (ring and nonring), organic acids and organic anhydrides, K2 = 4.358 For alkylbenzenes and polyphenyls(biphenyls, terphenyls) K2 = 4. 435 For cyclitols, alcohols(except diols, aromatic alcohols), K2 = 4.581 For all other compounds and gases, Where Tt - normal boiling point, K Tc - -critical temperature, K Pc - critical pressure, atm. This equation applies to nonpolar and polar liquids at their normal boiling points and gives average and maximum errors of 1.65% and 12. 2% respectively for 157 compounds.