The magnetic properties of ThMn₁₂-type Fe-rich compounds were investigated by producing Sm(Fe_0.8Co_0.2)₁₀Si₂ ribbons. The produced ribbons, with different conditions by varying the melt-spinning conditions, were characterized to investigate physical and magnetic properties. Weight fraction of ThMn₁₂-type phase decreased from 94.5 to 57.1 wt. % as the melt-spinning wheel speed increased from 6.5 to 39 m/s, and corresponding magnetizations and coercivities were substantially varied; the coercivity increased up to 0.175 T from 0.058 T by increasing the wheel speed from 6.5 to 26 m/s, and their magnetization also increased from 89.81 Am²/kg to 105.58 Am²/kg, even though the content of ThMn₁₂-type phase decreased. Morphologies of the ribbons were also observed to verify the melt-spinning effects on the surface conditions and grain sizes. It was found that the particle and grain sizes in the ribbons became smaller and striped patterns appeared as the wheel speed increased. The grain size decreased from about 1 μm to 250 nm by increasing the wheel speed from 6.5 to 39 m/s.