Most researches regarding emulsified fuel were in the areas of emulsifier, emulsified fuel manufacturing and emulsified fuel droplet combustion, but there were little papers published regarding emulsified fuel combustion and boiler efficiency in an industrial boiler. The main purpose of this study is to clarify whether improvements in the boiler efficiency and the reduction of pollutants such as CO, NOx, SOx and smoke exist or not when emulsified fuels are combusted in the commercial boiler. Main experimental parameters were water content in heavy oil , excess $O_2$, and boiler load. The fuels used in this experiment were 0.5 B-C, and 5 kinds of 0.5 B-C/water emulsified fuels. The combustion characteristics of heavy oil and its emulsions with water were investigated in an industrial boiler. The combustion stability was monitored and exhaust gases such as CO, NOx, SOx and smoke were measured with excess $O_2$ and combustion load. In case of emulsified fuel combustion, flame stability was poor and boiler efficiency was lowered by 1.6~5.7%, but emission levels of CO and smoke were improved.