We have developed Sm2Co17 sintered magnets whose Fe concentration is much higher than conventional Sm2Co17 sintered magnets. The pre-aging treatment leads to fine cell structure and improvement in squareness of demagnetization curves. As a result the (BH)max of pre-aged magnets shows higher than that of no-pre-aged magnet. The inter-mediate heat treatment (IHT) induces the grain growth. We found that squareness of demagnetization curve has clearly improved by the IHT at adequate temperature. These results indicate that reducing the fraction of grain boundaries by increasing the grain size affects the behavior of domain-wall motion. Sm2Co17 sintered magnets fabricated adopting pre-aging treatment and IHT show (BH)max of 282 kJ/m3.