Abstract: Because of the low fracture toughness，Ti(C，N) based cermets are limited for wider utilization in the field of cutting tools，carbon nano-tubes (CNTs) were deposited with Ni by electroless plating and the ultra-fine Ti(C，N) based cermets with various CNTs mass fractions were made by vacuum sintering in order to study the effect of CNTs on the fracture toughness of ultra-fine Ti(C，N) based cermets. The effect of different CNTs contents both Ni deposited and undeposited on the microstructure and fracture toughness of the cermets was studied. The micrographs observed by SEM show that coreless grains and micro pores exist in the cermets with CNTs. The results of fracture toughness conducted by indentation show that the addition of CNTs toughens ultra-fine Ti(C，N) based cermets by 29. 4 %～62. 7 %. Crack deflection，crack bridging，coreless grains and micro pores are responsible for the toughening mechanisms. In addition，the relative density and hardness of ultra-fine cermets decrease slightly with the increasing of CNTs mass fraction. CNTs both Ni deposited and undeposited can play an active role in improving the fracture toughness of Ti(C，N)cermets.