PURPOSE: To obtain Na2CO3 having extremely low apparent specific gravity, and high dissolution rate in water, by blending NaHCO3, with Na2CO3(calculated as anhydrous state), and an aqueous solution containing sodium silicate or CMC in a given weight ratio to give a blend, uniforming and calcining the blend in given temperature ranges, respectively.

CONSTITUTION: A blend is prepared in such a way that it has a ratio of NaHCO3:Na2CO3(calculated as anhydrous state):an aqueous solution containing sodium carbonate or carboxymethyl cellulose (CMC) of 1:(0.2W1.5):(0.1W0.8), especially 1:(0.3W1.5):(0.1W0.5) by weight. The blend is then stirred, kneaded, and uniformed at 40W105°C, especially at 50W100°C. The uniformed blend is then calcined at a sufficiently high temperature (100W300°C, preferably 150W220°C). Consequently, NaHCO3 is decomposed, and water containing sodium silicate or CMC is dehydrated, to give the desired Na2CO3. This Na2CO3 has 0.4W0.8 apparent viscosity, and ≤40sec dissolution rate in water, and it is extremely advantageous as a raw material component especially for synthetic detergent.