Poly(aspartic acids) of different chain lengths (11, 14, 18, 24, 30, 52, 58, ≈ 115) were prepared, for the use in aminoglycoside-induced nephrotoxicity inhibition studies, some in their pure L- or D-configuration and in pure α-linkage form by the polymerization of α-amino acid N-carboxyanhydride (NCA) derivatives with a variety of dialkyl aspartate molecules as primary amine initiators. The primary amine chosen served as an internal reference in the 1H NMR spectrum for the estimation of the degree of polymerization (chain length) in these molecules. Poly(aspartic acids) with varying amounts of D and L asymmetric centres and in pure α-linkage from were also prepared. Poly[(α-co-β)(L-co-D) aspartic acid] was prepared by a simplified thermal polymerization procedure for biological studies and also to study the tacticity effects in its 13C NMR spectrum. A qualitative correlation was demonstrated between the retention times from gel-permeation chromatographic analysis and the 1H NMR method used to estimate the polymer chain length.