The complex potential energy surface for the gas-phase ion-molecular reaction of the diborane(3) anion B2H3- with CO2, including 12 [B2H3CO2](-) intermediate isomers and 17 interconversion transition states, has been investigated theoretically at the B3LYP/6-311++G(d,p) and single-point CCSD(T)/6-311++G(d,p) levels. The CCSD(T) calculations show that for the B2H3- anion the single-H-bridged isomer HB(H)BH-is thermodynamically 4.7 kcal/mol lower in energy than the kinetically rather unstable nonbridged isomer H2BBH-. The thermodynamical and kinetical stability of these [B2H3CO2](-) isomers are determined, and the possible reaction pathways leading to five low-lying dissociation products (A) H3BBO- + CO, (B) c-BH2OBH- + CO, (C) H2BCO- + HBO, (D) H3BCO + BO-, and (E) c-BH2OCH + BO- are probed. It is shown that this reaction is initialized by the nucleophilic attack of B2H3- toward CO2, and all the five products are both thermodynamically and kinetically accessible. Our calculated results for the gas-phase reaction of the B2H3- anion with CO2 are in good agreement with the recent experimental results of Krempp et al., and may be helpful for understanding the chemical behavior of electron-deficient boron hydride anions.