The adsorptions of 2-(dimethylalkylammonio)propanoates with straight chain alkyl group having from 12 to 16 carbon atoms on the liquid-air interface were decreased while lowering the surface tensions at critical micelle concentrations. In micellization, the standard free energy changes per methylene in alkyl group were found to make same contribution to the micelle formation of corresponding C-alkylcarboxybetaines, and the standard enthalpy and entropy changes were studied within the range of temperature from 30 to $50^{circ}C$.