Prostitution was legal in the past, until Field Marshal Sarit Tanarat made it illegal in1960. This issue was again debated by Prime Minister Thaksin Shinawatra (2001-2005),but it could not be put on the government agenda. The purpose of this article is tostudy the reason why this issue was denied. Kingdom's agenda setting model consistingof political stream, problem stream, policy stream and policy window was applied.The findings could be concluded as follows: 1) the attitude of actors toward the problemin the political stream were different; 2) the problem was not urgent enough; and3) there was no consensus regarding a solution in the policy stream because the problemdid not go along with Thai values. Therefore, this problem could not go through the policywindow to be placed on the government's agenda. Finally, the government choseto keep prostitution illegal in Thai society, or deny legalizing prostitution.