I have observed the validity of open-offer from a point of European contract law in comparison with International Trade Law in this paper. Generally we know that an offer is an expression of willingness bo be bound to the contract. In English law if there are no intention it will be considered such as circulation of price lists or catalogues. As for French law these activities could be considered as an offer. However German law is closer to English law as to an offer. A contract which does not ascertained price is open-price terms and it can be applied not only for general commercial contracts but also for franchise or for distributorship agreements especially in Europe. When open-price terms applied to reserve a exclusive right to the contract the validity of contract can be a serious matter between principals. In English law an offer must be sufficiently complete to be capable of acceptaqnce. English law does not require that price terms should be indicated on offer. English law allow a open-price terms in the contract. In French law a contract will be valid in the absense of a price which is either determined or objectively determinable. A price by the market price of similar products is not enough to be valid offer. It should be recognized and accepted objectively by third parties. French law require that price terms should be indicated on offer. Open-price terms are not enough to be an effective offer. However German law shows more flexible than French law. In German law if the price is not fixed in the contract there are four ways to determine it. The seller may determine the price by the time of deliver. By reason of thess backgrounds I have made comparison with European contract law and International trade law on the validity of open-price offer in this paper. It seems that we are not familiar with open-price terms although franchise contract or special terms of contract have been increased in these days. So I hope this paper will be helpful to show a new point of view.