Global polarization of $Xi$ and $Omega$ hyperons has been measured for the first time in Au+Au collisions at $sqrt{s_{_{NN}}}$ = 200 GeV. The measurements of the $Xi^-$ and $bar{Xi}^+$ hyperon polarization have been performed by two independent methods, via analysis of the angular distribution of the daughter particles in the parity violating weak decay $XirightarrowLambda+pi$, as well as by measuring the polarization of the daughter $Lambda$-hyperon, polarized via polarization transfer from its parent. The polarization, obtained by combining the results from the two methods and averaged over $Xi^-$ and $bar{Xi}^+$, is measured to be $langle P_Xi rangle = 0.47pm0.10~({rm stat.})pm0.23~({rm syst.}),%$ for the collision centrality 20%-80%. The $langle P_Xi rangle$ is found to be slightly larger than the inclusive $Lambda$ polarization and in reasonable agreement with a multi-phase transport model (AMPT). The $langle P_Xi rangle$ is found to follow the centrality dependence of the vorticity predicted in the model, increasing toward more peripheral collisions. The global polarization of $Omega$, $langle P_Omega rangle = 1.11pm0.87~({rm stat.})pm1.97~({rm syst.}),%$ was obtained by measuring the polarization of daughter $Lambda$ in the decay $Omega rightarrow Lambda + K$, assuming the polarization transfer factor $C_{OmegaLambda}=1$.
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