Abstract A convenient, simple work‐up procedure and low‐cost chlorination method was developed to prepare sodium 5‐chlorotetrazolate dihydrate by chlorination of self‐prepared 1H‐tetrazole with sodium hypochlorite solution. Several organic extracting solvents and factors (raw material ratio, reaction temperature, and reaction time) were investigated to optimize the operating conditions of the chlorination procedure. These products were characterized by 1H and 13C NMR spectroscopy, vibrational spectroscopy (IR), mass spectroscopy (MS), and single‐crystal X‐ray diffraction. In addition, the thermal behaviors of the resulting sodium 5‐chlorotetrazolate dihydrate and sodium tetrazolate monohydrate were investigated and compared by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The results indicated that the optimum chlorination conditions were a stoichiometric raw materials ratio of 1:12:12 (1H‐tetralzole : sodium hypochlorite solution : acetic acid solution), a reaction temperature of 55 °C, a reaction time of 6 h, affording a 92.76 % yield; moreover, acetone was determined to be the best extraction solvent in terms of yield and toxicity. Crystal data: sodium tetrazolate, orthorhombic, Pmc2(1), a = 5.847(4), b = 5.605(3), c = 6.387(4) Å, V = 209.3(2) Å3, Z = 2, ρ = 1.746 Mg·m–3; sodium 5‐chlorotetrazolate, orthorhombic, Pnma, a = 6.8611(19), b = 6.9243(19), c = 12.281(4) Å, V = 583.5(3) Å3, Z = 8, ρ = 1.850 Mg·m–3. Sodium tetrazolate has a melting point at 275.97 °C and an exothermic decomposition peak at 319.45 °C, whereas sodium 5‐chlorotetrazolate shows only a sharp exothermic peak at 237.33 °C due to violent decomposition without melting.