The antitrust law or it is known in some jurisdictions, as competition law is the most important law to the market-oriented economic system nowadays. This is because the competition law helps creating and maintaining free trade and fair competition and sustaining market mechanism. Furthermore, the competition policy and competition law play a vital role in effectively facilitating the achievement of the goals of ASEAN economic integration. This paper aims to introduce structures and contents of competition laws in Thailand’s neighboring countries in the South, which are Singapore and Malaysia. The Competition Act is the main competition law in Singapore, which has its objective to promote the efficient functioning of the Singaporean market and maintain Singapore as one of the world’s most open and competitive economies by prohibiting anti-competitive business practices. The scope of the application of this act is to control anti-competitive behaviors of undertakings, which are any person whether an individual, a corporate, an unincorporated body of persons or any other entity that capable of carrying out commercial or economic activities relating to goods or services. Even state owned enterprises (SOEs) and government-linked companies are also included. This act also explicitly recognizes extraterritorial application. Most prohibitions of the Singapore competition act are in conformity with the international standards except anti-competitive vertical agreements. The Competition Commission of Singapore (CCS) is empowered to enforce this act. The enforcement performance of the CCS is impressive. The reasons behind this are partly because the CCS has sufficient powers and tools to enforce the competition law. The leniency program has been adopted in order to improve the capacity to detect cartels. After the adoption of the leniency program, the CCS can detect and penalize domestic and international cartel members. The anti-competitive conducts in Malaysia are governed by the Competition Act 2010 with its purpose to promote and protect the free and fair competition process and also the interests of consumers. Similar to the Singapore competition law, most conducts prohibited by the Malaysian competition act conform to the international standards. However, there is no merger control under the Malaysian competition regime. In spite of no merger control in Malaysia, undertakings are being advised not to engage in other kind of anti-competitive behaviors prohibited under this competition act, for example, the abuse of dominant position. The Malaysia competition law shares some similar characteristics with the Singapore competition law in the way that they both have the power to exercise their competition laws extraterritorially. Leniency programs have been adopted into both Singapore and Malaysia competition regimes in order to increase the capacity of competition authorities to detect cartels, which evidence and information relating to cartels are carefully kept in secret among cartel members. Malaysia Competition Commission (MyCC) is responsible for the enforcement of the competition act.