The surface and cross section morphology of rayon-based carbon fibers (RCF) and the resulting rayon-based activated carbon fibers (RACF) were investigated through scanning electron microscopy and atomic force microscopy. It was found that the surface of RCF exhibited grooves and striations with the width ranging from 30 to 90 nm, and the striation distribution was about 25 bars per µm around the circumference. While on the RACF, lots of pores emerged on the surface and superficial cross section (about 1 ~ 2 µm to the surface), namely, the external section was porosity but the interior section was close-grained. It was detected that the pore sizes ranged from 50 to 550 nm and the approximate pore distribution was 10 pores in 1×1 µm2. Furthermore, the walls of pores were not smooth but consisted of continuous grains with the diameters about 30 nm.