An experiment of diesel-butanol combined injection combustion, combining direct injection of diesel with port injection of butanol, was carried out on a research diesel engine. The effects of the butanol ratio on the emission characteristics were investigated at 1 400 and 1 900 r/min, and IMEP (indicated mean effective pressure), 0.5 and 1.0 MPa, respectively. The results have shown that butanol ratio is a key parameter for controlling diesel-butanol combined injection combustion. With the increase of butanol ratio, soot emissions are reduced, with a slight increase in NO-x- emission, but HC and CO emissions are increased markedly. When compared with the direct injection combustion of diesel-butanol blend-fuel, the diesel-butanol combined injection combustion is a major issue related to lower indicated thermal efficiency and higher HC emission. Therefore, future research is required for an improved manifold injection strategy.