Abstract: Pyrolysis derived bio-oil was emulsified by diesel oil with complex of nonionic surfactants. The density, calorific value, dynamic viscosity and pH value of the emulsified fuel were measured. The performance of bio-oil/diesel oil emulsified fuels with four different bio-oil/diesel oil ratios were tested on a SD1110 diesel engine, and the engine load characteristics and exhaust emission characteristics curves of diesel engine were determined. Then, the fuel economy and exhaust emission characteristics of the engine fueled with the emulsified fuel were analyzed in comparison with that of the pure No.0 diesel oil. The experimental results showed that the specific fuel consumption was the lowest, when the engine was fueled with the emulsified fuel containing about 20% volume fraction of bio-oil. CO emission of emulsified fuel was higher than that of diesel oil, and the high concentration of bio-oil was, the more CO emission was. But the NO and smoke emissions of the emulsified fuels were lower than that of the pure No.0 diesel oil. Since its physical and chemical characteristics are similar to that of diesel, bio-oil/diesel oil emulsified fuel can be used to fuel diesel engines.