(1) Patent troll refers to (2) non-practicing entities who (3) stack up patents or buy patent rights from other patent right holders to create a patent wall (4) with which they claim excessive license fee or compensation for damages against companies or exercise patent rights to file non-infringement litigation. It should not be forgotten that patent trolls’ profit-making by exercising patent rights does not always trigger cost increase or innovation loss to ultimately undermine consumer benefits. The term ‘patent troll’ always reflects some negative value judgment but bear in mind that it is used just for the purpose of companies sued in infringement litigation attacking patent right holders. Hence, an objective view is required to assess benefits and costs patent trolls bring with them rather than single-mindedly writing them off. The rights exercised by patent trolls are exclusive ones and it is up to patent right holders to decide license of patent on invention. This sets a platform on which ‘patent troll’ individual inventors or small companies, which are bound to be in a lower and disadvantageous position against large companies, can make the most use of their patent rights. Such could open ways to a new market model on patent rights trading, could help the weaker build capital with which they can file patent infringement litigation against large companies, cash in their inventions and eventually spur their appetite for new inventions. In other words, financial support to individual inventors and small companies provide incentives for new inventions, vibrate patent market through patent trading and make valid cases in patent infringement litigations. These are more than enough to appreciate the positive functions of patent trolls, which some patent funds or patent firms are trying to feed and nourish as part their policies to make good use of them. Not to mention, patent trolls should not be let free because some blinded by monetary benefits could kill developers’ drive for new R&D, stand in the way of innovation and technological breakthroughs, blurring purpose of patents to drive industrial advance and improve people’s welfare. Stacking patents with ambiguous effect, filing infringe- ment litigations over such patents, act of unfair reconciliation, of demanding unreasonably high license fee or charging discriminative license fee when his/hers becomes technical standards are all in breach of Anti-trust Law, and which need regulations. This, however, does not mean that they can be clamped down immediately with Antitrust Law. Legal regulations can only be levied when claiming non-infringement of his/her patent rights unfairly expands market control and erodes consumer benefits and when unfair trading requires sturdy control to the extent of requiring government intervention. Holdup act could constitute as abuse of market dominant position disturbing price abuse in Clause 1, interfering other companies' business activities in Clause 3 and impeding participation of new competitors in Clause 4 of Article 3-2(1) of Antitrust Law if patent trolls have a dominant market power and restriction of competition is acknowledged. Even if dominant market position or restriction of competition are not acknowledged, they can also be regulated subject to unfair luring of customers (Clause 3, Article 23(1)) in unfair trade act of Article 23 or interfering other companies' business activities (Clause 5, Article 23(1)). Unlike coercion in dealings and abusing dominant position, unfair luring of customers does not require the act which is acknowledged to be oppressive. However, it is at least needed to cause adverse effect on free competition in the market. Antitrust interventions are not recommendable without any anticompetitive or adverse effect in the market hindering fair trade order or at least oppressiveness of the behaviors.