Calcium carbonate (CaCO3) particles have been used in various applications, including medicine, drug delivery and orthopedics. Having three different polymorphs and exhibiting complex crystallization behavior, it is a challenging task to systematically control physical properties of CaCO3 particles for desired applications. Herein, the influence of pH and [Ca2+]:[CO32-] ratio on the morphology, size and polymorph of room temperature synthesized CaCO3 particles were investigated. Although, in literature, ethylene glycol concentration of precursor solutions is considered as one of the most critical factors controlling polymorph and morphology of CaCO3 particles, present work highlights precursor solution pH to be a stronger factor in controlling room temperature synthesized CaCO3 particle properties. In fact, CaCO3 particle size decreased from micron to sub-micron range and calcite polymorph transformed to vaterite upon decreasing pH of the precursors for all of the precursor solution [Ca2+]:[CO32-] ratios investigated in this study. Importantly, CaCO3 particles with different and distinct morphologies were obtained by altering pH and [Ca2+]:[CO32-] ratios of the precursor solutions. Since requirements for the physical properties of CaCO3 particles are diverse for industrial and medical applications, it is important to understand CaCO3 crystallization behavior for tailored particle synthesis. (C) 2018 Elsevier B.V. All rights reserved.