Effects of phase changes on 3He release/retention and crystal lattice evolution during aging of erbium (Er) tritide films were investigated using X-ray diffraction. The contents of α phase and γ phase in the Er tritide films showed significant different effects on 3He release/retention. The initial tritium stoichiometry or excess tritium atoms accommodated in the octahedral sites and the microstructure (i.e., the texture and Er2O3 oxide inclusions) played an important role for the 3He release and the evolution of 3He bubbles in the β phase Er tritide films. In the β + γ region, evolution of 3He in the β phase was apparently influenced by the γ phase, which could result in a strongly anisotropic lattice dilation and an earlier inflection point of the expansion rate of (1 1 1) lattice parameter. A preferred occupation of 3He in basal plane of the hexagonal γ phase and the lattice expansion along the hexagonal direction were identified.