Effects of the nitrogen addition on high temperature tensile properties and creep resistance of the fully lamellar and the duplex Ti-48.5Al-1.5Mo (at.%) alloy were investigated. High temperature yield strength of the nitrogen-doped alloys increased due to solute hardening and precipitation hardening of Ti3AlN. Nitrogen addition led to remarkable improvement of creep resistance in the duplex microstructure as well as in the fully lamellar microstructure. In particular, the primary creep deformation of the 1.0 at.% nitrogen-doped alloy with the duplex microstructure decreased definitely to a similar or superior level of the fully lamellar alloy. We consider that precipitate hardening of p-phase (Ti3AlN) and solute hardening of nitrogen atoms may be responsible for such remarkable creep resistance of the nitrogen-doped alloys. (C) 2000 Kluwer Academic Publishers.