The surface tensions and densities of aqueous solutions of oxalic, malonic, succinic, maleic, malic, and cis-pinonic acids were measured as a function of the acid mole fraction at 25 degrees C. These organic acids are typically found in atmospheric aerosols. The surface tensions were measured using the Wilhelmy plate method and were measured also as a function of temperature. The measurable mole fractions were limited by the solubilities of the acids at room temperature. All the acids lower the surface tension of pure water. cis-Pinonic acid lowers the surface tension most effectively. The measured surface tensions were fitted with equations covering the acid mole fraction range from zero to one and assuming a theoretical surface tension of pure, supercooled acids at room temperature. The measured densities were also fitted in a similar way. These equations can be used in model calculations of formation and growth of atmospheric particles.