Wool/cotton union fabric was dyed with a direct dye in union shade. The dyeing was performed in a single bath in relation to four factors: leveling agent (Lyogen SMKI, 0-1.5 % oww), electrolyte (sodium sulfate, 0-10 %), dyeing temperature ($85-95^{circ}C$), and dyeing time (15-60 min). The dyeing was characterized by dye bath exhaustion (%), color strength (K/S value), washing fastness, and light fastness of dyed sample. Response surface analysis showed that the exhaustion of direct dye increased with electrolyte, dyeing temperature, and dyeing time while the K/S value followed a linear shape with leveling agent and dyeing temperature. An optimized recipe was formulated based on response surface strategy and numerical optimization solution.