The in-situ titanium nitride (TiN) coating with a great thickness was reactive plasma sprayed in a nitrogen-containing environment. The microhardness of the coating was measured, and the indentations were used to determine the fracture toughness of the coating. The toughening mechanism was characterized by analyzing the SEM morphologies of TiN coating's fracture surfaces. Results show that the coating possesses a high hardness and toughness. The average hardness of the coating is 1200H(V) (100) (g); and the fracture toughness (K-IC) of it is 4.51 MPa center dot m(0.5). The cross-section of the TiN coating shows an obvious phenomenon of indentation size effect (ISE). The toughening mechanisms of the coating are crack deflection and pores, etc. (c) 2004 Elsevier B.V. All rights reserved.