The surface tensions and densities of aqueous solutions of dimethylamine, (CH3)2NH, and sulfuric acid, H2SO4, were measured at 24.2 °C. Mol fractions of dimethylamine were varied between 0 and 0.21 and of sulfuric acid between 0 and 0.48. The surface tension of the binary dimethylamine + water solution decreased exponentially as dimethylamine was added, from the surface tension of water (72 mN·m-1 at 25 °C) to the value of 34 mN·m-1 at the maximum dimethylamine mol fraction of 0.21. The surface tension of the ternary system did not change from that of water + sulfuric acid until a sufficient amount of dimethylamine was added to turn the solution alkaline. When the mol fraction of dimethylamine was more than double the mol fraction of sulfuric acid, the surface tension of the solution started to approach that of water + dimethylamine. Polynomial fits were applied to measured data sets of both surface tension and density. Results and fitting parameters are presented.