After the subprime mortgage crisis of 2008 of America, shareholder's derivative litigation has a tendency to increase. The reason is that financial institutions have great loss due to excessive risk-taking. Shareholders blamed the directors for failure to monitor or oversee financial institution' excessive risk-taking. Actually, the duty to monitor is closely related to the occurrence of harm to the corporation arising from wrongdoing, illegality, or other harmful activities. A director is, therefore, obliged to monitor and oversee whether or not officers or employees commit wrongdoing or violate laws and regulations. A breach of the duty to monitor may impose oversight liability on directors. The legal standard in respect of a breach of the duty to monitor is the Caremark Duty that the Delaware courts have developed. Specifically, the Delaware Chancery Court in the Caremark case held that the board of directors should have a responsibility to establish internal control in the context of oversight. Generally speaking, the duty to monitor has been explained in the scope of duty of care. By the way, the duty to monitor became a kind of duty of loyalty through duty of good faith under the Stone case that the Delaware Supreme Court decided. In case of recent derivative suits, a legal issue is whether or not the Caremark Duty applies to the cases related to failure to monitor business risk. In the Citigroup's derivative litigation, the Delaware court held that oversight duty does not apply to business risk. The reason is that business risk may protected under the business judgement rule. Under JPMorgan Chase & Co. derivative litigation, the federal court made a decision according to the legal doctrine in respect of director's oversight liability of Delaware. The federal court held that a plaintiff should prove director's bad faith with particularity, so the plaintiff lost the case. However, the Delaware doctrine of the duty to monitor should be criticized in some points. First, the duty to monitor in Caremark dose not induce active and effective director oversight. Second, the scope of the duty to monitor is limited. Third, a plaintiff has difficulty in winning a case because a plaintiff must prove bad faith. Fourth, in the context of financial institution's regulation, financial institutions director's oversight liability is not appropriate under the Delaware doctrine. Lastly, the standard of review in respect of a breach of the duty to monitor is too easily avoided to provide substantial deterrent effect. It is, therefore, very difficult to improve director oversight in a meaningful way because the standard of review actually eliminates the threat of liability.