In this study, the effects of experimental conditions on the facile morphosynthesis of CaCO3 were investigated. The analyzed conditions included the pH, concentration, mixing and aging temperature, and aging time. After establishing the optimal conditions for calcite and aragonite formation, the effects of organic additives, i.e., PVP, PDDA, PEG, CTAB and EDTA, on the stability and morphology of both polymorphs were examined. Finally, the applicability of calcite as a filling material in polyester was tested. The results indicated that calcite was optimally synthesized at pH 9.0, 0.05 M initial reactant concentration, and 30oC mixing and aging temperatures while the aging time was 24h. The morphologies of produced calcites were dominated by rhombohedra and cubic with particle size range of 5-6 m. On the other hand, the precipitation of CaCO3 dominated with aragonite requires mixing and aging temperatures of 70-90 in addition to shorter aging times. Within such experimental condition, aragonites displayed needle-like and branch-like morphologies with ca. 95% aragonite fraction and aspect ratio of around 8. The applied additives demonstrated various effects on the morphology of precipitated CaCO3. These effects ranged from changing the particle morphology of calcite and aragonite up to suppression of aragonite formation. Finally the application of calcite as a filler in polyester polymer is discussed in light of a comparative determination of mechanical and thermal properties.