A simple formula of estimating the standard hydrous enthalpy of cation and anion,Δ_hH^θ_m(M^n±) was presented. The errors between calculated and reported values of Δ_hH^θ_m(M^n±) was within 8%. The standard enthalpies of formation of cations and anions with known Δ_hH^θ_m(M^n±) and Δ_fH^θ_m(M^n±,aq,∞) or Δ_fH^θ_m(M^n±,g), Δ_fH^θ_m(M^n±,g) or Δ_fH^θ_m(M^n±,aq,∞) were estimated by the formula established.