The particle sizes of calcium carbonate (CaCO3) produced by the chemical crystallization method were reported to be almost always larger than 3 µm. An experimental setup was developed to crystalize CaCO3 from sodium carbonate (Na2CO3) and calcium chloride (CaCl2) solutions in a plug flow reactor (PFR) with a retention time of 9 seconds and added into a stabilizing solution of calcium hydroxide. The CaCO3 particles were produced with a size larger than 13 µm in the PFR tubular reactor. Effect of cations such as hydroxide form of sodium (Na+), potassium (K+), calcium (Ca++), and barium (Ba++) as well as anions such as the sodium form sulfate (SO4=), nitrate (NO3-), carbonate (CO3=) and bisphosphate (HPO4=) were investigated. While cations produced calcite particles at sizes larger than 2 μm in the presence of Na+and K+ ions, nano-calcite particles in the presence of Ca++ ions. A new crystalline form, Barytocalcite (BaCa(CO3)2), and whitherite (BaCO3) particles were produced in solution containing Ba++ ions. The size and morphology of vaterite and calcite particles did not change as particles in the PFR tubular reactor in the presence of SO4=, NO3-, and CO3=ions. Different crystal forms were synthesized in the presence of HPO4=ion. These formations clearly indicated the dissolution and recrystallization of CaCO3 particles. A novel technique was devised for the continuous production of nano-CaCO3. It was demonstrated that nano-calcite particles of about 350 nm were produced by the chemical method not previously reported in the literature.