The biradical mechanisms of furan pyrolysis proposed by Lifshitz and Mackle were investigated by ab initio calculations. Critical structures of the proposed mechanisms were optimized by UMP2/6-31G(d,p), and energies were evaluated by the G2(MP2) method. The activation energies of the biradical channels were predicted more than 10 kcal/mol higher than both available experimental values acid the activation energies of a non-biradical mechanism we studied before. The calculated activation entropies of the biradical channels are very close to the calculated activation entropies of the non-biradical channels. These results indicate that the biradical mechanism is unlikely more competitive than the non-biradical mechanism.