The HCN formation mechanism during the O-2 gasification of Blair Athol coal char is examined at 600 degreesC. A nitrogen-free phenol resin char is also used as a reference char sample, to examine HCN formation during the reaction with NO/O-2 mixed gas at the same temperature. It is concluded that, in both systems, the nitrogen-containing surface species (C(N)) has an important role as a reaction intermediate for HCN formation. The HCN formation temperature, 600 degreesC, is much lower than that for the reaction without O-2. In the temperature-programmed desorption experiment, a high temperature (> 900 degreesC) is also necessary for HCN formation. An important role of O-2 in enhancing HCN formation is to activate C(N) via breakdown of the carbon network. In the resin char/NO/O-2 reaction, the evolution of HCN is not influenced by the removal of NO from the feed gas. This result shows the importance of C(N) as an intermediate for the HCN formation.