Octyl-, decyl- and dodecylbetaines, CnH2n+1CHCOO-+N (CH3)3(n=8, 10, 12), were synthesized from appropriateα-bromo-fatty acids and trimethylamine. The reaction mixture was purified through many steps, and the final product was obtained as a colorless crystal. The progressive purification through each step was traced by infra-red absorption and paper chromatography. It was shown by pH-titration and also by electrophoresis that these betaines exist as Zwitterions in a from slightly acid to strongly alkaline solution. The critical micelle concentrations determined by the solubilization of Sudan III were 0.085, 0.0098 and 0.0011 mole/l for octyl, decyl- and dodecylbetaines