Abstract: Calcium（II） complexes including Ca（Butala）₂, Ca（Hexala）₂, Ca（Octala）₂, Ca（Decala）₂, and Ca（Dodala）₂, were meticulously synthesized through a precisely orchestrated reaction between calcium hydroxide （Ca（OH）₂） and distinct ligands, namely butanoylalanine （HButala）, hexanoylalanine （HHexala）, octanoylalanine （HOctala）, decanoylalanine （HDecala）, and dodecanoylalanine （HDodala）. Among these, Ca（Octala）₂, Ca（Decala）₂, and Ca（Dodala）₂ stand out as recently synthesized compounds. Guided by a meticulous exploration of their solubility, phase transition temperatures, and thermostability, we embarked upon the preparation of CaCO₃ nanoparticles. This involved a precisely orchestrated process wherein Ca（II） complexes were subjected to the reactive influence of CO₂ gas fluxing, thereby facilitating the creation of the desired CaCO₃ nanoparticles. The synthesis resulted in CaCO₃ nanoparticles of varying shapes, with their size diminishing from 64 nm to 10 nm as the alkyl chain length of Ca（II） complexes increased from C4 to C12. This size reduction could be attributed to the aggregated Ca（II） complexes molecules in a methanol or methanol with small amount water solution. The hydrophobic interaction of Ca（II） complexes intensified with longer alkyl chains, contributing to the reduction in nanoparticle size. This implied that the manipulation of alkyl chain length and size of ligand could yield CaCO₃ nanoparticles exhibiting varied sizes and morphologies. Importantly, the synthesis method for CaCO₃ was environmentally sustainable due to the utilization of a raw material derived from amino acids. The Ca（II） complex, serving as the precursor, is readily accessible, underscoring the efficiency of this approach. This approach offers novel insights for the green synthesis process of nano-grade CaCO₃. Owing to its excellent properties, nano-grade CaCO₃ as a new material holds broad prospects in scientific research and industrial applications.