The concept of highly-flowable concrete was developed from the transformation of underwater concreting ideas to the concreting structures on land. Therefore, the general properties of highly-flowable concrete are similar to those for concreting under water. The viscosity of highly-flowable concrete is high so that segregation of the coarse aggregate from the concrete can be eliminated. The slump flow of highly-flowable concrete is greater than 600mm so as to increase its flowability. The slump flow is defined as the diameter of slumped concrete. The distinctive feature of the mixture is that a larger proportion of fine material is used in it. The high viscosity and large amount of fines increases its resistance to segregation. In the method of mixture proportioning of highly-flowable concrete proposed by the authors, a high-range water-reducing admixture (HRWRA) is used in order to increase the slump flow. Furthermore, a segregation-reducing agent is used to minimize the segregation although a large proportion of fines somewhat increases the viscosity of concrete. Limestone powder, which is a relatively low reactive material, is used to reduce the heat of hydration and shrinkage. In the proposed method of mixture proportioning, it is possible to choose the required average strength, water content and fine aggregate-total aggregate ratio to suit special and particular conditions of concrete structures under various environmental conditions.