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The magnetic properties and crystal structure of melt spun SmCo7-xSnx (x=0-0.6) ribbons have been investigated. The XRD patterns of ribbons spun at a high wheel speed of 40 m/s show that a pure TbCu7-type structure is formed only for x=0.1, while a mixture of CoSn appears at the grain biundary for x ≥ 0.2 and 2:17 phase appears for x ≥ 0.4. The Rietvield refinement result shows that Sn prefers to occupy the 2e sites in TbCu7-type structure, which is similar to Ge. The coercivity of melt spun SmCo7-xSnx ribbons is enhanced from 1.9 kOe for x=0 to 8.4 kOe for x=0.3 . The grain size is reduced with Sn substitution from 100-400 nm for SmCo7 ribbons to 50-100 nm for SmCo6.7Sn0.3 ribbons, which also contributes the coercivity in addition to the enhancement of magnetic anisotropy field by the occupation of Sn atoms at 2e sites.