Objective To improve the mechanical properties of SiC fibers. Methods PBeCS was used as the precursor, and SiC fibers containing beryllium were produced by polymer-derived method. SEM, XRD and tensile strength tests were carried out. Results SiC fibers containing beryllium had a diameter between 20 to 30 μm, and their surface was smooth. With a tensile strength of 600 ~700 MPa, the fibers were not as good as the current commercial SiC fibers, however, after being treated under 800 ℃ for 2 h in the air, SiC fibers containing beryllium had an increase of over 30% on tensile strength, and without obvious changes in sur- face morphology. These fibers kept more than 90% strength after being treated at 1100 ℃ for 2 h in the air. However, after being treated at 1200 ℃ for 2 h in the air, cracks appeared on the surface of the fibers, along with a sharp decrease of tensile strength. When the temperature of heat treating rose, the tensile strength of ordinary SiC fibers kept decreasing which was always lower than that of SiC fibers containing beryllium. During the heat treatment in the air, a SiO2 layer appeared on the surface of Be-SiC fibers, but not on the surface of ordinary SiC fibers. Conclusion The reason for good mechanical properties of SiC fibers containing berylli- um under high temperature in the air may be that beryllium caused the oxidation of SiC to generate SiO2 on the surface of fibers, which prohibited inner materials from being oxidized, and meanwhile strengthened the surface of the fibers.