To investigate the combustion characteristics of a swirling diffusion gas burner with oxygen enrichment, mean temperature, CO, $CO_2$, and HC concentrations were measured at various oxygen enrichment conditions. According to the results, the flame temperature increased and the region of high temperature was expanded with increasing oxygen concentration. The $CO_2$ concentrations increased, while the CO concentrations decreased in proportion to the increase of oxygen concentration. On the other hand, the HC concentrations were decreased and this tendency was very strong at the downstream of the combustor.