Polyethylene (PE) was exposed to tritium gas at about 1 atm pressure. Low density polyethylene (LDPE) was more labeled than high density polyethylene (HDPE) was. Tritium labeling was enhanced at higher temperature. The rate of specific activity of HDPE was 2.5×108 Bq/g atm hr. n-Eicosane was molded to a small spherical shape, and the activity depended on the surface area and the averaged specific activity was 7×107 Bq/g atm hr.