Statistical theories of fracture of brittle materials have been applied to ceramics under mechanical loading conditions. In this paper, the retained strength after thermal shock was analysed theoretically and the probability of crack occurrence of ceramics was predicted. In this analysis, the Weibull statistical theory of fracture was applied to thermal shock of ceramics on the assumption that thermal shock fractures of ceramics were due to crack growth from one of the initial flaws. For the purpose of verification of this proposed analysis, thermal shock tests on three kinds of ceramics using liquid sodium as the quenching medium were performed. As a result, analytical results were good agreement with results of thermal shock tests. Thus, the probability of crack occurrence can be evaluated with the normalized fracture strength using effective volume and effective stress hold time.