The high-temperature resistant Si-Al-C-(O) fibers were prepared through polymer-derived method using continuous polyaluminocarbosilane (PACS) fibers. Evolutions of the crystallization during the pyrolysis of the Si-Al-C-(O) precursor fibers were investigated by a series analysis. The structure of the fibers transforms from organic state to inorganic state and the crystalline phases appear during the pyrolysis. The beta-SiC crystallite size increases when the temperature is higher than 1,300 degrees C. At the same time, the alpha-SiC appears. At 1,600 and 1,800 degrees C, the grain size of beta-SiC of the fibers is 15.4 and 22.1 nm, respectively. The growth of beta-SiC and the appearing of alpha-SiC have a great influence on the properties of the fibers. The change of the tensile strength of the pyrolysis products is divided into three stages with the growth of the crystal. The tensile strength of the Si-Al-C fibers is higher than 1.9 GPa.