The presence of tars during biomass gasification is a major problem in the gas-processing systems and internal combustion engines. In order to develop a technology for the reduction of tars at low temperatures, the reactivity of active oxygen species O- in the oxidative decomposition of biomass tars using a 12CaO center dot 7Al(2)O(3)(C12A7) crystal was investigated experimentally. The C12A7 was used as a less expensive carrier of O- radicals. Tars were produced from pyrolyzed wood chips at 1273 K and decomposed in the presence of C12A7/O- in a stream of pure nitrogen gas at 623-673 K. The results showed that the tars could be oxidized in the presence of C12A7/O- at a temperature of 623 K or above, which may not be achievable by other methods.