Tritium (T) uptake by exposure to gaseous T on deuterated C deposition layer on W was investigated. The C deposition layer were prepared by mixed D and C ion irradiation. The specimens were exposed to D an T mixed gas at 423 and 573 K. The additional T retention by gas exposure at 573 K was about 4 times higher than that by gas exposure at 423 K. Further heating from 573 to 673 K in vacuum after the gas exposure, resulted in more than 70% of retained T stayed after heating at 673 K. That should be due to changing of nature of trap sites in C deposition layer during experiments. These results suggest that additional T trapped in such trap sites require higher temperature to remove retained T in such trap sites. (C) 2014 Elsevier B.V. All rights reserved.