In the present study, the Sm₂Fe₁₇N_x-type interstitial materials have been prepared by reaction between Nb-free or Nb-containing Sm₂Fe₁₇-type alloy and N₂ gas. Nitrogenation behaviour of the Sm₂Fe₁₇N_x-type material and disproportionation characteristics of the nitrogenated materials have been studied by means of differential thermal analysis (DTA) and thermopiezic analysis (TPA). Magnetic properties of the produced Sm₂Fe₁₇N_x-type interstitial materials were characterised in vibrating sample magnetometer (VSM) or thermomagnetic analyser (TMA). Epoxy-bonded or Zn-bonded Sm₂Fe₁₇N_x-type magnets were prepared, and their magnetic properties were investigated. It has been found that nitrogenation kinetics of the Sm₂Fe₁₇-type alloy is improved significantly by the Nb-substitution for Fe in the alloy. The Nb-substitution is also found to enhance thermal stability of the Sm₂Fe₁₇N_x-type interstitial material. Hard magnetic properties of the interstitial materials produced from Nb-free orNb-containing alloy is high enough (intrinsic coercivity : over 7 kOe) for application as bonded permanent magnets. The good hard magnetic properties of the interstitial material are maintained in the epoxy-bonded magnet. Intrinsic coercivity of the Zn-bonded magnets is improved significantly as post-bonding annealing time increases.