The pyrolytic reaction between tetraethylammonium chloride and potassium boro-hydride in the presence of water was used for the preparation of B₁₀H₁₀^2- and B₁₂H₁₂^2- anions in one step.The effect of reaction temperature, time and the amount of water used on the yield was studied in order to determine the optimal reaction conditions for the preparation of B₁₀H₁₀^2-.When the reaction was carried out at 1870 for 16 hrs.and 210° for 1 hr.,the yield of B₁₀H₁₀^2- was shown to be 79% (37%) and 63%(29%) respectively,When the reaction temperature was below 170°,there is no B₁₀H₁₀^2- formed.