In this study, the effect of thermal oxidation on the lattice parameters of Ti–4Al–2V alloy was studied.Samples were oxidized at 450, 600 and 650 °C for 1–7 h in electric furnace under air atmosphere. The lattice parameters were determined using the Cohen method as a function of oxidation time at each temperature. The lattice parameters of as-received alloy are calculated as a = 0.29289 nm and c = 0.46652 nm. The thermal oxidation at 450 °C results in a gradual increase in a-parameter, whereas it goes through a maximum at higher temperatures(600 and 700 °C). The results show that these maximums are reduced to an approximately constant value after a long-time oxidation. The c-parameter generally increases over the whole treatment condition. It is believed that these variations could be due to the dissolution of oxygen atoms in octahedral sites of hcp lattice of titanium. In this study, the effect of thermal oxidation on the lattice parameters of Ti-4Al-2V alloys was studied. Samples were oxidized at 450, 600 and 650 ° C for 1-7 h in electric furnace under air atmosphere. The lattice parameters were determined using the Cohen method as a function of oxidation time at each temperature. The lattice parameters of as-received alloy are calculated as a = 0.29289 nm and c = 0.46652 nm. The thermal oxidation at 450 ° C results in a gradual increase in a -parameter, it it through the maximum at higher temperatures (600 and 700 ° C). The results show that these maximums are reduced to an approximately constant value after a long-time oxidation. The c-parameter generally increases over the whole treatment It is believed that these variations could be due to the dissolution of oxygen atoms in octahedral sites of hcp lattice of titanium.