Mineralogical studies play a key role in deciphering mineral’s formation and associated geochemical processes in geosciences. This paper presents the application of Raman spectroscopy to the characterization of actinolite in rock samples. The studied actinolite was formed as the pseudomorph of primary pyroxene in gabbrodiorite intrusive rock sample collected from Varan area, Urumieh-Dokhtar Magmatic Arc of Iran. The Raman spectra of micrometer-sized actinolite grains embedded in a crude rock sample are compared with the corresponding literature data for actinolite and tremolite in range of 200-1200 cm-1 and 3600-3700 cm-1 region. The results show that the quantitative estimation of Mg# = Mg/(Mg+Fe2+) can be obtained from the fractional intensities of the OH-stretching bands by applying Raman spectroscopy to micrometer-sized actinolite grains in a crude rough rock sample, which is in good agreement with the results from EMPA. The Raman spectroscopy is a fast method and low-cost for quantitative estimation of Mg# in actinolite.