As one of the main hydration products, Ca(OH)2 has important effects on mechanical properties and durability of hardened cementitious materials. In this study, Ca(OH)2 precipitates were synthesized by continuous feeding of CaCl2 and NaOH solutions into a bulk solution containing triethanolamine (TEA) or diethanolamine (DEA). Analytical techniques including electric conductivity measurement, TOC, ICP − OES, XRD, FTIR and SEM were employed to investigate the impacts of the alkanolamines on the precipitation process and morphology of the synthetic Ca(OH)2. Results show that TEA strongly hinders the nucleation and growth of Ca(OH)2 precipitate due to the complexation effect with Ca2+ ions in solution. The chemical incorporation of TEA into the lattice structure greatly disrupts lattice structure of the obtained Ca(OH)2 precipitates and alters the morphology from typical hexagonal prism of pure portlandite to vertically stacked or randomly agglomerated Ca(OH)2 lamellae crystals with much smaller size. In contrast, DEA exhibits little effect on the precipitation process and morphology of portlandite.