The abnormal conditions encountered by an iran-based high-temperature water-gas shift catalyst in different processing stages and the effect of these conditions on the mechanical strength of the catalyst have been investigated by experimental simulation and Weibull statistics. In the process of production, heating and reduction, the catalyst can often be over-heated. Over-heating or thermal treating of the powder before pelleting as well as the pellets, and thermal shock in the reduction lower the mean horizontal crushing strength and the Weibull modulus, and increase the probability of strength failure by 3 to 10 orders. Absorption of moisture and wetness by water of the pellets, and steam or water shock in the reduction increase this probability by several orders. The mechanical treatment by dropping down the pellets on the floor also lowers the strength. The results in this paper show that properly pelleted and reduced samples possess a very high and reliable strength, for instance, the best reduced sample has a Weibull modulus up to 12.8. The probability of failure of this sample at 10 kg/pellet is as low as 4.16 . 10(-11). These results show the potentiality in increasing catalyst mechanical strength, and show that due to their brittleness, the catalysts should be properly processed.