The densities of CO_2 inclusions in minerals are commonly used to determine the crystallizing conditions of the host minerals.However,conventional microthermometry is difficult to apply for inclusions of small size(<5-10μm) or low density.Raman analysis is an alternative method for determining CO_2 density,provided that the CO_2 density-Raman shift relation is known.This study aims to establish this CO_2 density-Raman shift relation by using CO_2 inclusions synthesized in fused silica capillaries.By using this newly-developed synthetic technique,we formed pure CO_2 inclusions,and their densities were determined by microthermometry.The Raman analysis showed that the relation between CO_2 density(D in g/cm3) and the separations(△in cm~(-1)) between the two main bands(i.e.Fermi diad bands) in CO_2 Raman spectra can be represented by a cubic equation:D (g/cm~3)=0.74203(-0.019⊿~3+5.90332⊿~2-610.79472⊿+21050.30165)-3.54278(r~2=0.99920).Our calculated D value for a given⊿ is between those obtained from two previously-reported equations,which were derived from different experimental methods.An example was given in this study to demonstrate that the densities of natural CO_2 inclusions that could not be derived from microthermometry could be determined by using our method. The densities of CO_2 inclusions in minerals are commonly used to determine the crystallizing conditions of the host minerals.However, conventional microthermometry is difficult to apply for inclusions of small size (<5-10μm) or low density. Raman analysis is an alternative method for determining CO_2 density, provided that the CO_2 density-Raman shift relation is known. This research aims to establish this CO_2 density-Raman shift relation by using CO_2 inclusions synthesized in fused silica capillaries.By using this newly-developed synthetic technique, we formed pure CO_2 inclusions, and their densities were determined by microthermometry. Raman analysis showed that the relation between CO_2 density (D in g / cm3) and the separations (Δin cm -1) between the two main bands (ie Fermi diad bands in CO 2 Raman spectra can be represented by a cubic equation: D (g / cm 3) = 0.74203 (-0.019⊿ -3 + 5.90332⊿ ~ 2-610.79472⊿ + 21050.30165) -3.54278 (r 2 = 0.99920) .Our calculated D value for a given⊿ is betwee n both obtained derived from two previously-reported equations, which were derived from different experimental methods. An example is given in this study to demonstrate that the densities of natural CO_2 inclusions that could not be derived from microthermometry could be determined by using our method.