This paper suggests a method for designing robotic mixed product lines as an expert system. The expert system consists mainly of the production rules for the following procedures. (1) To settle a kind of robot to be set in each work station and the position to set it. (2) To settle the position/posture of works. (3) To assign "complex elemental works" to the robots. The rules were created from the viewpoints of maximizing the efficiency of performing desired production plans and minimizing the numbers of work stations and stations for changing the posture of works.