This study is to clarify the substance of Ch’en Tu-hsiu’s scientific thought. The study focuses on Ch’en Tu-hsiu’s ideological conversion with his basic recognition and partially examines the nature of Chinese Scientism. In his days, not simple changes on social system but fundamental conversion of perception was required to break an old customs and construct a new society. He discovered the basis of the perception on scientific thought. For him, science was ‘power of thought’ and a means to revolutionize the era and the society as the motivity for an ideological conversion. First, he suggested scientific world view for the basis of ideological perception. He urged Chinese who were imbued with old customs and ignorance at that time to convert their awareness and perception through scientific reason. Furthermore, he asserted destruction of organic view of nature, personified nature, the relativistic theory of Yin and Yang(陰陽說), adults in idolization (聖敎,聖言), religious superstition etc. not to disturb the development of Natural Science. Second, he sought a way to social reforms reflecting the social function of science by expanding natural sciences to social sciences. He insisted human liberation based on human rights theory, stressed out the progress of mankind through social Darwinism, demanded the conversion of the scientific empirical era by accepting Comte’s the History Development theory and the maximization of the utility of things by imposing utilitarianism. Third, he proposed scientific socialism as a feasible alternative associating the concept of social science with practical logic. After reviewing five types of socialism, he ruled out anarchism without a means of revolution - national authority - for the priority, and also regarded Syndicalism and Guild-socialism based on the anarchism as immature socialism forms. Fourth, he compared national socialism(social democracy) and communism for viable socialism types. From his perspective, communism was preferred to national socialism. Because he thought that the former was based on the alliance between labor and management, parliament politics, democratic politics, nationalism etc., whereas, the latter was founded on class struggle, direct action, proletarian dictatorship and the international movement, and it was more corresponding to「Doctrine」of Marxism. He also considered that under scientific cognition, historical perception of scientific socialism enabled the establishment of socialist economic system in the country which formed the national superstructure on the basis of the material conditions. In the May Fourth era, beginning with human thought liberation and human modernization, he made a comparison with eastern, western scientific perspectives, and his scientific thought finally presented modern scientific view point significantly taking account of independent reason and formal logic. By these, he converted Chinese scientific point of view from ancient one to modern one. His new scientific idea encouraged to develop and change the Chinese modern scientific thought, and brought about results progressing and reinforcing the trend of Chinese scientism during the period.