In　situ　X-ray　diffraction　measurements　for　natural　Fe-bearing　and　Fe-free　Mg2SiO4　forsterite　single-crystals　((Mg1.83Fe0.17)SiO4　and　Mg2SiO4)　were　performed　with　diamond　anvil　cell　high-pressure　device　and　synchrotron　radiation　X-ray　diffraction　at　room　temperature.　The　experimental　results　showed　that　no　phase　transition　of　two　natural　olivine　single-crystals　was　observed　within　the　upper　highest　pressure　of　9.9　GPa.　The　isothermal　relationship　of　pressure　and　volume　in　the　two　kinds　of　crystals　is　well　described　by　the　second-order　Birch-Murnaghan　equation　of　state　with　the　zero-pressure　unit　cell　volume　and　zero-pressure　bulk　modulus　of　0.292　9(3)　nm3　and　140(3)　GPa　for　Fe-bearing　forsterite　and　0.289　9(1)　nm3　and　151(2)　GPa　for　Fe-free　forsterite,　respectively.　The　linear　compressibilities　along　a,　b　and　c　axes　(ka,　kb　and　kc)　are　elastically　anisotropic　in　the　two　kinds　of　forsterite　and　the　anisotropy　can　be　described　as　kb>kc>ka.　With　the　addition　of　iron　into　the　crystals,　the　bulk　velocity　of　olivine　decreases　and　the　difference　between　the　two　kinds　of　forsterite　single-crystals　is　5.2%.　This　result　will　be　significant　for　the　study　of　the　composition　of　the　earth＇s　upper　mantle　and　its　elastic　wave　velocities.　©　2016,　The　Editorial　Board　of　CHINESE　JOURNAL　OF　HIGH　PRESSURE　PHYSICS.　All　right　reserved.