Titanium nitridation in liquid nitrogen has been investigated by heating titanium wires electrically with various electric powers to make clear the reaction characteristics and the possibility of self-sustaining reaction occurrence. It has been possible to define the critical electric power necessary for an initiation of Ti wire combustion. The value was determined to be 1.58 W/mm(2) for the wires 0.1 similar to 0.3 mm in diameter tested in the present work. The temperature of the combustion initiation was confirmed to be close to the melting point of Ti. The Ti wire heated at the critical electric power in liquid N-2, could be almost completely nitrided within one second.