In this paper, we investigate a possible mechanism to control a mobile robot via a sensory-motor coupling utilizing chemical system. To find the characteristic of correlation between the diffusion process of the chemicals and the behavioural patterns, we simulated the diffusion process and the kinematics of the robot. In comparison to Braitenberg vehicles in which sensory-motor coupling is tightly realised by hardwiring, our system employs soft-coupling. The mobile robot has two sets of independent sensory-motor units, two distance and light sensors are implemented in front and one motor on each side of the robot. The environment was constructed with a surrounding wall and a light source located at the center. Depending on the design parameters and initial conditions, the robot was able to successfully avoid the wall and light. More interestingly, the diffusion process in the sensory-motor coupling provided the robot with a simple form of memory which would not have been possible with a control framework based on a hard-wired electric circuit.