The CISG has been effective since January 1,1988. Even if both parties of international sales contract are located in ratifying countries, the CISG does not apply to certain excluded transactions. The CISG does not apply if the parties have opted out of the CISG. When the parties opt out, they usually agree on the law that is to replace the CISG. In the context of international sales, the frequent and difficult choice of law problems will arise when the CISG applies to a transaction but does not resolve all the legal issues before the tribunal. So this article deals with the question. What should we select the applicable law in such situations? (1) For products liability issues excluded from the CISG by article 4 and 5, the court should apply the substantive law of the market state and the statute of limitations law of the forum, (2) For validity issues excluded from the CISG by article 4(a). the court should apply the UNIDROIT Principles when its rules resolve the issue.