Non-discrimination principle in the GATT/WTO legal system is principally composed of the principles of most-favoured nation treatment and national treatment of Articles 1 and 3 of ‘GATT 1994.’ The former principle requires WTO member countries to equally treat all the like products traded among them. The latter principle obliges importing countries to equally treat their like domestic products and imported products from any other member countries. Therefore, non-discrimination obligation can be only applied to so-called like products according to the relevant provisions. Diverse concept and scope of the like products, however, have been suggested through the GATT practices and history without clear definition in any provisions of the GATT/WTO legal system. Among the provisions in which the term like products are included, Article 3 of ‘GATT 1994,’ the fundamental provision of the national treatment, has been main source of controversy concerning the concept of like products in the GATT and WTO dispute settlement cases. In particular, GATT panels and WTO panels and Appellate Body have not clarified their attitude in determining the standards and factors of the like products to which the national treatment principle of Article 3 of ‘GATT 1994’ applies. Traditionally, GATT panels have adopted the objective standards, such as physical character, quality, and function of products, in deciding the likeness of products. They, however, for a while, had determined the likeness based on a policy objective-oriented approach with special reference to the aim-and-effect of the internal measures in question. Presently, WTO panels and Appellate Body are taking the GATT’s traditional position, rejecting the aim-and-effect test. Both traditional and aim-and-effect test approaches have respective merits. The former approach would be more conformity with the free trade doctrine because it only concerns whether there are any results or effects of protecting domestic production regardless of the intents and purposes behind the internal taxation and regulation. On the contrary, the aim-and-effect test approach will comparatively narrowly interpret the concept and scope of the like products to which the national treatment principle of Article 3 applies. As a result, this approach will be more favorable to the member countries’ autonomy in discriminating products and taking various internal measures according to their policy objectives. However, despite the above-mentioned several virtues, it should be noted that the aim-and-effect test approach ⅰ) has no legal grounds ⅱ) disregards the special structure and characteristics of Article 3, ⅲ) commits a serious mistake in disapproving the differences of the meanings, scopes and concepts of each provision and word constituting Article 3, ⅳ) permits member countries to enforce protective measures more easily, ⅴ) negates the legal meaning of Article 20, ⅵ) unreasonably imputes a burden of proof to the improper party, and ⅶ) allows the member countries to determine the likeness of products under their subjective intents and purposes. This approach will result in injuring the normative purposes of Article 3. Thus, the recent WTO’s approach, rejecting the aim-and-effect test but adopting the traditional objective approach, will be more reasonable. To conclude, accordingly, in determining the likeness of products in the national treatment principle of Article 3, it is more desirable to employ the objective standards, rejecting the subjective ones such as the aims or effects of the measures in question.