During the period of colonialism in Southeast Asia, Thailand tried to preserve its sovereignty through modernization. One of the most important phenomena which appeared during this period in Thailand was discussion on parliamentarism. Parliamentarism was regarded as an efficient framework of political system to operate modern state. The issue of parliamentarism was the most sensitive and as such the most serious theme in discussions on political reform and modernization of Thailand from 1885 in the reign of King Chulalongkorn to the early 1930s in the reign of King Prajadhipok. The discussion of parliamentarism was at last realized through the 1932 revolution, which changed the traditional political system of absolutism to constitutionalism. This study, which introduces and analyzes various ideas of Thai elite and common people on parliamentarism from the late nineteenth to the early twentieth century, can contribute to the understanding of historical background and character of constitutionalism in Thailand.