The thermal power generation is one of main generation of electricity in Japan. The fuels of thermal power generation are coal, oil and liquefied natural gas. While the price of coal is stabilized, the emission rates of CO₂ , SOx, NOx, dust and soot from coal fired power station are very large compared with other fossil fuels. Integrated coal Gasification Combined Cycle（IGCC）is new technology of coal fired power generation with low environmental impact. In IGCC, the gas is produced from the coal at the gasifier, and the electricity is generated by combined cycle. The coal gasification slag is collected from the gasifier in IGCC. In this study, the application of coal gasification slag to fine aggregate for concrete was investigated. Two types of coal gasification slag, which were original and grinded slag, were used for the tests. From the test results, the physical properties of coal gasification slag, especially grading and particle shape, were improved by grinding slag particle. Both original and grinded slag had no effect on the fresh properties of concrete when the substitution rate of slag was 25％. However, the substitution rate of slag was over 50％, slag concrete showed little tendency of segregation in spite of low water content. The air content of slag concrete was very low within a range of 1.1 to 1.4％. The strength properties of slag concrete were equal to or greater than concrete without slag when the substitution rate of original slag was less than 25％.高い発電効率を持つ石炭ガス化複合発電では、石炭灰がガラス状の石炭ガス化溶融スラグとして排出される。本研究は、石炭ガス化溶融スラグのコンクリート用細骨材への適用性について検討を行った。試験では、排出されたままの未処理スラグと磨砕処理を行った磨砕スラグの2種類を用いた。試験結果より、スラグを磨砕することで細骨材としての物理的性質は向上し、特にスラグ全体の粒度、粒形が改善されることが分かった。本研究で使用した2種類のスラグでは、置換率25％程度であればコンクリートの練上がり状態および強度特性に対して大きな影響は及ぼさなかったが、空気量はスラグの種類や置換率に関わらず、約1％の低い値を示した。