As promising light-weight high-temperature materials, g-TiAl base alloys are considered as prospective candidates for automobile and aerospace application due to their high specific yield strength. Adding Nb to TiAl alloys increases the liquidus temperature and results in improvents of creep resistance, high temperature strength and oxidation resistance. High Nb-containing TiAl alloys have attracted much attention during past decades. With the addition of carbon in Ti-46Al-8Nb-xC alloys (x=0, 0.7, 1.4, 2.5, atomic fraction, %), the formation of precipitates, the orientation relationship between precipitates and the TiAl matrix and the evolution of the precipitates during heat treatments have been investigated in this work by XRD, SEM and TEM. The results show that lath-shaped precipitates of Ti₂AlC can be formed during the preparation of ingots with the addition of 1.4% and 2.5% of C. With good thermal stability, the size, amount and distribution of Ti₂AlC precipitates remain almost stable during the aging process. Needle-shaped precipitates of Ti₃AlC are formed in the aged alloys with 0.7%, 1.4% and 2.5% of C. And the precipitates are preferentially formed in g grains. The orientation relationship between Ti₃AlC precipitates and g phase is found to be {100}_Ti3AlC //{100}_γ and <001> _Ti3AlC //<001>_γ. Meanwhile, the precipitation behavior and morphology of Ti₃AlC are also discussed. Ti₃AlC precipitates grow slightly after prolonged aging, while the amount of the precipitates remains small. With a higher aging temperature, the size of Ti₃AlC precipitates increases significantly and an increasing amount of the precipitates is observed.