Abstract. X-ray absorption spectrum (XAS) and X-ray magnetic circular dichroism (XMCD) in a filled skutterudite SmOs₄Sb₁₂ were measured at Os L-edge under multiple extreme conditions, T = 2.2 K, H = 10 T, and P up to 3.5 GPa in order to obtain information of Os 5d electronic states. At ambient pressure, small dichroic signal of 0.1% was clearly observed and the orbital and spin magnetic moments of Os 5d are estimated to be -0.001 μ_B and 0.012 μ_B, respectively. At high pressure, the XMCD intensity reaches a maximum around 0.6 GPa, and decreases with increasing pressure as to finally disappear at 3.5 GPa. This trend is similar to the reported magnetization under high pressure. The behavior of Os 5d electronic states strongly connects with a novel feature observed in SmOs₄Sb₁₂.