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It is known that high fluidity concrete performs much higher fluidity, segregation resistance and placeability than normal concrete. However, it is hard to apply high fluidity concrete made with existing method in field because of high manufacturing cost and complicate quality control. For working out this problems, The author made segregation-reducing type superplasticizer(SRA) by using superplasticizer, viscosity agents and AE agent, and manufactured high fluidity concrete with flowing concrete methods applying it. It is thought that application of fly ash make possible to manufacture high fluidity concrete using SRA with more economical profits. Therefore, this paper is intended to investigate the influences of fly ash and segregation-reducing type superplasticizer on the properties of high fluidity concrete. Tests are conducted on high fluidity concrete, made with base concrete using fly ash and developed superplasticizer. Dosage of superplasticizer and fly ash contents are varied. According to experimental results, As dosage of superplasticizer and fly ash contents increase, fluidity, segregation resistance and placeability show positive results. And also compressive strength at early age shows to be retarded, while it gains high strength at later age, compared to that of plain concrete. Reducing dosage of superplasticizer and improvement of quality of high fluidity concrete are available by applying fly ash in the range of about 20%.