The present communication reports a pH-dependent facile synthesis of calcium aluminum layered double hydroxide (CaAl-LDH), at 3 different pH conditions of 8.5, 10.5 and 12.5 respectively, by simple coprecipitation route that led to the precipitation of the same in phase pure or in mixed phase form, and their detail characterization. Interestingly, at a pH of 8.5, the precipitate obtained was 100% phase pure CaAl-LDH, represented as sample A, whereas, at higher pH conditions, a mixed phase comprising 37% of a combination of CaCO3 polymorphs, e.g., calcite and aragonite and 63% of the CaAl-LDH (at pH 10.5, represented as sample B) and 43% of a combination of calcite and aragonite and the rest 57% being CaAl-LDH (at pH 12.5, represented as sample C) respectively, were obtained. The increasing trend of the presence of carbonate anion (with reference to calcite and aragonite phases) was estimated by trace level ion-exchange chromatography study using organic acid column. All the above samples were tested for their anticancer activity in vitro, using cancer cell lines, e.g., human colon carcinoma (HCT116) and human breast adenocarcinoma (MCF7). Interestingly, sample A only exhibited significant growth inhibition of the cancer cells as above-mentioned. The observation as above was verified using human osteoblast precursor cells (MC3T3) as well, on which, all the samples (sample A, sample B and sample C) exhibited good cellular viability.