The X-ray diffraction (XRD) of C2H5OH molecules confined in slit-shaped graphitic micropores of activated carbon fibers having different pore widths was measured at 303 K. The effect of the pore width in the range 0.7-1.1 nm on the molecular assembly structure of C2H5OH in the micropores was examined. The XRD patterns were analyzed by use of the electron radial distribution function (ERDF) analysis. The densities of C2H5OH molecular assemblies in micropores were determined by C2H5OH adsorption at 303 K and N-2 adsorption at 77 K. The density of C2H5OH molecular assemblies in the 0.9 and 1.1 nm pores was close to the solid density of C2H5OH. The ERDFs showed that the first and second nearest-neighbor peaks shift to a shorter distance with a decrease of the pore width while their peak heights increase. These changes of the ERDFs coincided very well with the adsorbed density of C2H5OH, indicating that the serious confinement by the micropores gives rise to the solidlike ordering even at 303 K.