Copper smelting slag has been produced in large quantities every year all over the world. However, currently, development of new utilization of slag has been desired because production of slag has been increasing. The objective of this study is recovery of useful metals such as iron, copper, zinc, etc. from the copper slag. Generally, it is difficult to recover useful metals from the slag since it exists as an amorphous structure because of rapid cooling by water. However, they can be separated and concentrated by physical separation when they are crystallized and grown in their grain size. In this study, we investigated effect of slow cooling to crystalize the Fe contents as magnetite and recover it as Fe resources or carrier of other dilute useful elements. We prepared synthetic slag which consisted of Fe and Si. The slag was heated at 1,573 K for 1 hour in N2 atmosphere and slowly cooled at open cooling and 10, 3 and 1 K/min of cooling rate in super kanthal furnace. As a results, crystallization of magnetite and fayalite was confirmed when they were slowly cooled. Results of SEM-EDS/MLA analysis showed that yield and grain size of magnetite were increased with decreasing cooling rate. When cooling rate was 1 K/min, 80 % of average diameter of magnetite particles in the slag reached to 120.7 μm, whereas it was 5.3 μm at open cooling. Furthermore, we tried simplified wet magnetic separation test to investigate selective separation of magnetite from resulting slag. Results of magnetic separation showed that recovery, grade and separation efficiency of magnetite were increased with decreasing cooling rate. When the cooling rate was 1 K/min, above 90 % of recovery, 44.1 % of grade and 50.7 % of separation efficiency of magnetite was obtained. These results suggested that slow cooling is effective for magnetite recovery by magnetic separation.