This paper describes mobile manipulation of humanoid robots. A humanoid robot is a kind of integrated machines: a two-arm and two-leg mechanism. It could be well applied to mobile manipulation in non-routine task automation. The main objective of the mobile manipulation is to obtain versatile and efficient manipulation by the arms. In this respect the legs are required to assist the arms obtaining their high manipulability by changing step length and tim-ing of step motion. The required motion of the legs in mobile manipulation is different from the conventional biped locomotion. From this point of view, we discuss and analyze the required motion of legs in mobile manipulation. We propose a basic idea to quantitatively evaluate robot performance in mobile manipulation. Because manipulability and stability vary during the robot motion, we take an average and a variance of manipulability measure of arm, and an average and a minimum of stability margin per a locomotion cycle as an evaluation criterion. By computer simulations, the relationship between these evaluations and some patterns of leg motion is analyzed by using the proposed control method of mobile manipulation. The simulation results show that the leg motion can vary the manipulability of the arm by changing the step length and the timing of the step motion. It is also found that the manipulability of the arm and the stability of the robot are closely related.