High temperature oxidation and oxidation-induced embrittlement in β-silicon carbides (SiCs) with different grain boundary microstructures have been studied. SiCs with different grain boundary microstructures were fabricated by hot-pressing with different doping elements like Mg, Al, P. Oxidation experiments were carried out under the oxygen partial pressure ranging from 0.303 Pa to 78.5 Pa at temperatures 1623—1773 K for 7.2—36 ks. Thereafter, the degree of oxidation-induced embrittlement was quantitatively evaluated by three-point bend tests at room temperature in connection with grain boundary microstructure. More severe degradation was observed as a result of oxidation though the passive oxidation took place. It is concluded that the oxidation-induced embrittlement in β-SiC can be improved by decreasing the frequency of random boundaries and the grain size. The potential of grain boundary engineering for a ceramic material has been confirmed.