The rate of oxidation of tantalum in 1 atm of purified oxygen was measured at three temperatures between 475° and 530°C. The oxide was initially protective but became nonprotective as oxidation progressed. This kinetic behavior was correlated with metallographic and electron optical studies of oxidized Ta specimens, and it was shown that the oxide films became non‐protective through the formation of microscopic blister ‐like cracks in the oxide. A comparison between the oxidation characteristics of Ta and Nb is given.