Co-liquefaction of a Chinese bituminous coal with bagasse - a biomass waste - has been carried out in an autoclave of 300-ml capacity at a temperature range of 350-450 degreesC, reaction time 15-45 min and cool hydrogen pressure 300-700 psig (2.04-4.76 MPa). The addition of baggasse and tetralin are beneficial to liquefaction. Optimization of the co-liquefaction process was carried out with respect to oil yield by the Factorial Experiment Design Method. The oil yield reached 48% at optimum conditions of temperature 420 degreesC, cool hydrogen pressure of 500 psig and reaction time of 40 min. A polynomial mathematical model-second order response surface model has been obtained for correlating the oil yield response factor as well as conversion with the major process variables. The equation derived by us holds well in determining the effect of process variables on response factors for any regime condition in the range of our experimental design within +/- 5%.