Er doped Si represent an interesting class of materials for the realization of light emitting devices based on Si technology. The local structure around Er ions is known to strongly affect the luminescence properties of the Rare Earth. In this work the Er site in Er+ O doped silicon samples prepared by Molecular Beam Epitaxy has been investigated by x-ray Absorption Spectroscopy at the Er L III edge. Samples with different preparation parameters such as the O/Er ratio and thermal treatments were investigated. Data were fitted using a model consisting in a first shell of O atoms and a second shell of Si atoms and accounting for multiple scattering effects. The rare earth is found to be linked to 5–6 O atoms at around 2.23 Å whereas a well defined Er-O-Si bond angle of≈ 136 deg is evidenced.