This paper aims to introduce an overview of the regime of expert witness in the medical malpractice litigation, and to provide a plan of how to make it improved. In regard with medical expert witness, several problems, such as time-consuming procedure, non-neural and unclear opinion without reasons provided, have been pointed out for several years. Lack of skill of the court and plaintiff/defender to question the expert is one of many cause to lead to the above problems. What is questioned to the expert? Because expert witness is used in determining probability of negligence, questions to the expert should be selected on the grounds of whether or not to obtain opinions or facts sufficient to let the judge infer negligence in view of the theory of proof burden established by the Supreme Court. In addition, to avoid non-neutral and unclear opinion, it is necessary to question the expert clearly, specifically and scientifically.