This study aims to find a correlation between XRD and Raman result of the activated carbon fibers as a function of its activation degrees. La of the isotropic carbon fiber prepared by oxidation in carbon dioxide gas have been observed using laser Raman spectroscopy. The basic structural parameters of the fibers were evaluated by XRD as well, and compared with Raman result. The La of the carbon fibers were measured to be 25.5 Å from Raman analysis and 23.6 Å from XRD analysis. La of the ACFs were 23.6 Å and 20.4 Å, respectively, representing less ordered through activation process. It seems that the ID/IG of Raman spectra were related to crystallite size(La). Raman spectroscopy has demonstrated its unique ability to detect structural changes during the activation of the fibers. There was good correlation between the La value obtained from Raman and XRD. Keywords : Raman, XRD, La, Crystallinity, Activation