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Racemic R.S α arylethylamine was resolved by R(-)thiazolidine 2 thione 4 carboxylic acid, a new resolving agent abbreviated as , by which R(-)TTCA·S(-) arylethylamine salts 2a - 2e, 20 D= -47.24°_-64.40° and optically active R(+) α arylethylamines 3a - 3e , 74.54%_94.45% e.e., were obtained. Optically active S(-) α arylethylamines 4a - 4e , 72.84%_90.36% e.e., were obtained by the decomposition of 2a - 2e in basic solutions. The influence of substitutive group of the benzene ring on the basicity of the amino group was studied by semiempirical PM3 method. The structures of the R(-)TTCA·S(-) α phenylethylamine salt (2a(R S) configuration) and R(-)TTCA·R(+) α phenylethylamine salt (2a′(R R) configuration) have been established by means of X ray diffraction. They crystallize in a monoclinic system. Space group is P 2 l. The cell constants of 2a(R S) configuration were obtained as follows: a =1.387 8(2), b =0.664 05(10), c =1.580 0(2) nm; β =90 844(10)°, Z=4 ; those obtained for 2a′(R R) configuration were a= 1.080 6(2), b =0.584 80(12), c = 1.218 8(2) nm, β =110.38(3)°, V =0.722 0 nm 3, Z =2. There are intermolecular hydrogen bonds in the crystals of the two kinds of configurations of the amine salt. The hydrogen bond number in the unit cell of R(-)TTCA·S(-) α phenylethylamine salt is twice as much as that of R(-)TTCA·R(+) α phenylethylamine salt.