America and the other developed countries in the game industry have been discussed the regulations of adult games in the view of freedom of expression. However, in Korea, adult games have not been developed because of social moral judgement and regulations for the reason of child protection. Adult games which could contain some sexually-lewd and pornographic contents should be concerned in the sense of adults` right to enjoy and freedom of expression. For that, it is significant to look for directions of improving adult game contents as taking different discourses to protect children from the violent and lewd games in America, analyzing American game history on the view of regulation and expression and comparing achievement of the contemporary game GTA to failure of 3feel and REVERSE-ONLINE The movement of consultation from the private-self regulations to the government restrictions among the developed game countries shows that it is needed to have comprehensive countermeasures and definite regulation of mature game contents as on the delicate position of selling online games out of the country. Since the adult games are researched and set up with the market-oriented views, it has been insufficient in preventing the reverse function of adult games. The market trend of adult games is important, but it is more valuable to recognize the reverse function of game cultures which have been neglected to increase domestic gamers and pioneering foreign markets. Accordingly, to improve adult game industry, it is needed to make continuous studies about the culture of advanced game countries, share information among the industry-academia and research centers as analyzing game structure and research the institutional and legal regulations and the culture of advanced game countries.