It is known that lichens are used for assessment of atmosphere pollution by heavy metals, radioniclides, sulfur and nitrogen oxides, etc. However there were published in scientific literature only limited data on usage of lichens as bio-indicators of tritium1,2. There are presented in the paper the results of lichen application study for assessment of atmospheric pollution by tritium. Both tritium in tissue free water (TFWT) and organically bound tritium (OBT) were measured in lichen. Lichen species Hypogimnia physodes was used as a basic bioindicator. Pieces of lichen were sampled within the distance of 30 km of emission source. Established sampling sites were rectangular in shape with linear dimensions 100*100 m. Lichen samples were sampled from various trees: birch tree, aspen tree, pine tree and linden tree at the level of 1.5 m above the ground. Thermal vacuum desorption technique was used to extract TFWT from lichen samples. Pyrolitic oxidation of dried lichen samples by vanadium oxide was used to extract tritium from OBT. Air monitoring stations equipped with active and passive samplers were used to sample HT and HTO from the atmosphere. Liquid scintillation counting was used to measure tritium content in water samples. It was determined that tritium content in lichen samples (both in TFWT and OBT) in vicinity of an emission source is higher than that of tritium content in lichen at distant sampling sites. Variation of tritium activity of TFWT was about 10 times, variation of tritium activity in OBT was about 70 times. It was supposed that tritium content in TFWT was in equilibrium with tritium content in atmosphere at the minute of sampling, while tritium content in OBT was determined by tritium content in atmosphere over longer period of time.