Activated carbon fibers (ACFs) were prepared by steam activation of windmill palm (WP) (Trachycarpus fortunei) fibers in a nitrogen atmosphere at various temperatures in the 600 to 850 °C range, and their characteristics were investigated. The effects of temperature, in terms of porous texture and surface chemistry, were identified through the use of scanning electron microscopy (SEM), nitrogen adsorption-desorption, mercury intrusion porosimetry (MIP), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. The results showed that the ACFs prepared at relatively high temperatures presented more cracking, collapsed surfaces, and lower yields because of the violent reaction that occurred during the activation process. With increasing temperature, more micropores were generated, and then the number eventually declined because of the conversion of partial micropores into mesopores. The ACFs with the highest special surface area, 1320 m2/g, and total pore volume, 1.416 cm3/g, were obtained at the activation temperature of 850 °C. In addition, graphitic carbon, the main compound on the surface of ACFs, decreased. Conversely, the amount of functional groups containing C-O (except for C-OH) slightly increased with increasing activation temperatures. It was also found that the mesopore volume and methylene blue adsorption of ACFs were highly increased as the temperature increased from 600 to 850 °C. Accordingly, WP fibers are a promising precursor for ACF production.