Four novel amphoteric surfactants of N-(2-alkylamidoethyl)-N, N-dimethyl ammonioacetates were synthesized. The each reaction between four saturated fatty acids containing 10, 12, 14 and 16 carbon atoms and N, N-dimethylethylene diamine permitted to give the intermediate products, N-(2-alkylamidoethyl)-N, N-dimethylamines. Quaterinzation of these intermediates was permitted to form N-(2-alkylamidoethyl)-N, N-dimethyl, ammonioacetates, whose sturctures were identified by CC, TLC, elemental analysis, IR pectrophotometry and $^1$HNMR spectrometry. The products yielded from 48% to 58%. The isoelectric points were shown in the range of $4.30{sim}6.64$. It showed a tendency to learn to the acidic site and its range was broadened as increase of the hydrophobic group length. Surface tensions of the aqueous solution in the $10^{-6}{sim}10^{-1}$mol/l of amidobetaines were measured. and the critical micell concentration(cmc) were shown in the range of $8.37{ imes}10^{-6}{sim}8.96{ imes}10^{-2}$mol/l, and ${Gamma}_{cmc}$ were reduced to 32.3~38.2 dyne/cm. A linear relationship between log cmc and the number of carbon in the hydrophobic alkyl chain was presented by the formula of log cmc=2.38-0.5n, and the contribution-rate of n on the standard free energy change in micellization ${partial}({Delta}G^0$$_m)/{partial}n$, was calulated as -0.5RT.