Co-Re catalyst (Co : Re = 1 : 4) prepared by reduction of cobalt nitrate hydrate and ammonium perrhenate mixture with ammonia at 973 K was very active for ammonia synthesis (2.4 mmol h(-1) g(-1)) at 623 K under 3.1 MPa (N-2 + 3H(2), 60 mL min(-1)) in spite of extremely low surface area (<0.5 m(2) g(-1)).