A converter slag has been heat-treated above melting point at reduced condition by cokes. As the result, most iron was separated. To make hydraulic compounds, calcium oxide was added to the reduced converter slag and the mixtures were sintered. This modified converter slag clinker mainly contained tricalcium silicate and calcium aluminates, and have a great potential to be a good hydraulic cement. The hydrates of the hydraulic compounds and gypsum with and without granulated slags, were mainly C-S-H, ettringite, calcium monosulfoaluminate hydrate, calcium aluminate hydrate, and $Ca(OH)_2$