Ternary B-C-N amorphous and crystalline coatings were deposited by microwave chemical vapor deposition using a mixture of NH3, CH4, B2H6 and H2 gases at substrate temperatures in the range 800-1350°C, and a gas pressure in the range (9.0-12)×103 Pa. We studied the influence of deposition conditions (i.e. gas composition, substrate temperature and material) on the coating structure, chemical composition and surface morphology. Both amorphous and polycrystalline coatings were deposited. Amorphous coatings were usually formed at lower substrate temperatures and were non-homogeneous across the coating thickness. Nanocrystalline inclusions of boron carbide, boron nitride and diamond were observed in amorphous B-C-N compounds. Polycrystalline coatings were generally represented by both diamond and boron nitride phases. In one case, a polycrystalline coating with the composition of B2CN4 was fabricated. The experimental results are discussed in detail. © 2001 Elsevier Science B.V. All rights reserved.