Abstract A series of experiments has been designed and conducted to study the effect of three operating factors, namely, coal feedrate, coal particle size, and steam/O 2 ratio, and their interactions on the quality of syngas produced from fluidized bed gasification of lignite coal. The quality of syngas is evaluated based on five indices including carbon conversion, H 2 /CO ratio, CH 4 /H 2 ratio, gas yield, and gasification efficiency. The design of experiment tool based on the response surface methodology (RSM), which is believed to be more accurate than the common one-factor-at-a-time approach, is used to facilitate the comparison of the effect of all factors. The factors are tested in the ranges of 0.036–0.063 g/s, 70–500 μm, and 0.5–1.0, for coal feedrate, coal particle size, and steam/O 2 ratio, respectively. The carbon conversion, H 2 /CO ratio, CH 4 /H 2 ratio, gas yield, and gasification efficiency are found to range from 91% to 97%, 0.776 to 1.268, 0.0517 to 0.0702, 3.4 to 3.7 m 3 gas/kg coal, and 56% to 67%, respectively. The effects of individual operating factors and their interactions on each syngas quality index are discussed using RSM tools. A set of operating conditions to achieve syngas with a desired quality for different applications is also proposed by optimization of the response surface of each index.