Switchgrass was co-fired with coal in an industrial scale boiler to investigate the co-firing effects on boiler performance and pollutant emissions. Comparing with firing coal alone, co-firing with switchgrass slightly lowered boiler efficiency by 0.6 to 1% under full-load and low-load conditions, respectively. Net carbon dioxide and SO2 emissions were reduced with co-firing. Nitrogen oxides (NOx) emissions were similar with co-firing to firing coal alone under both high and low loading amounts of switchgrass. Varying the nitrogen content by changing switchgrass type and harvest time revealed no significant effect on NOx emission in the range of tested conditions.