In this study, a newly developed duplex coating method incorporating plasma carburization and CrN coating was applied to Ti-6Al-4V and its effects on the creep and high temperature fatigue were investigated. The creep resistance was enhanced significantly by the duplex surface treatment. The stress exponent and the activation energy for creep of duplex-surfacetreated Ti-6Al-4V at 510~550°C were measured to be 8.0-9.5 and 230 to 280 kJ/mol, respectively. Both the stress exponent and the activation energy were not appreciably changed by surface modification suggesting that the creep deformation mechanism is not modified by the surface treatments, but rather dominated by the deformation of the Cu matrix. In the temperature range of the present study, the β phase acts as an athermal obstacle and increases the athermal strengthening component, which would increase the creep resistance and the stress exponent. Since the creep deformation proceeds by overcoming thermal obstacles in the matrix, the activation energy is not appreciably modified by the presence of the β phase. The fatigue of duplex-surface-treated Ti-6Al- 4V improved significantly over that its non surface-treated counterpart. The initiation of fatigue cracks is likely to be retarded more effectively by the presence of hard and strong Cr layers on the surface, resulting in life time enhancement.