We have developed a bilateral controlled micro-manipulator system for medical application. By operating this system, an operator can perceive the stiffness of small part of tissue by his/her tactile sense, and the visco-elastic parameters of the tissue are identified from the measurements of the displacement and the reaction force of the slave. Firstly, the relation between the tactile sense and the identified visco-elastic parameters is experimentally obtained. And then, using this relation, a method which evaluates the stiffness of the tissue by means of the fuzzy reasoning is proposed.