There are provided a magnetic tunnel junction structure and a method of fabricating the same. The magnetic tunnel junction structure includes a lower electrode, a lower magnetic layer pattern and a tunnel layer pattern, which are sequentially formed on the lower electrode. The magnetic tunnel junction structure further includes an upper magnetic layer pattern, a buffer layer pattern, and an upper electrode, which are sequentially formed on a portion of the tunnel layer pattern. The sidewall of the upper magnetic layer pattern is surrounded by an oxidized upper magnetic layer, and the sidewall of the buffer layer pattern is surrounded by an oxidized buffer layer. The depletion of the upper magnetic layer pattern and the lower magnetic layer pattern in the magnetic tunnel junction region can be prevented by the oxidized buffer layer.