H₂B₁₀H₁₀ was prepared via an ion exchange reaction using [(C₂H₅)₄N]₂B₁₀H₁₀ as raw material. Six novel heterocyclium decahydrodecaborates,[3-amino-1,2,4-triazolium]₂[closo-B₁₀H₁₀],[4-amino-1,2,4-triazolium]₂[closo-B₁₀H₁₀],[1-H-1,2,3-triazolium]₂[closo-B₁₀H₁₀],[benzotriazolium]₂[closo-B₁₀H₁₀],[1-methylimidazolium]₂[closo-B₁₀H₁₀] and [urotropinium]₂[closo-B₁₀H₁₀] were synthesized by the reaction of H₂B₁₀H₁₀ and the heterocyclic compounds or urotropine. All yields were up to 90%. The structures of the products were characterized by IR,¹H NMR,¹³C NMR and elemental analysis. Thermal properties of six kinds of target compounds were investigated by DSC and TG. The effect of nitrogen heterocyclic cation on the thermal stability of heterocyclium decahydrodecaborates was preliminary discussed. Results show that the decomposed temperatures of six kinds of target compounds are 232.6,274.6,176.1,211.0,219.4 and 164.9 ℃,respectively. The melting temperature of [4-amino-1,2,4-triazolium]₂[B₁₀H₁₀] is 72.8 ℃,which is an energetic ionic liquid with better thermal stability. The stronger alkaline and the higher density of electron cloud for the cationic precursor nitrogen heterocyclic compounds are beneficial to improve the thermal decomposition temperature of the target compounds.