This study was conducted to investigate the 2 week-oral toxicity of Paecilomyces sinclairii in Sprague-Dawley rats. P. sinclairii was daily administered to male and female rats for 2 weeks with different dose levels (0, 0.008, 0.04, 0.2, 1 and 5 g/kg). There were no clinical signs compared with control group, but a slight increase of white blood cell (WBC) was observed in the males rats receiving all dose levels of P. sinclairii. In biohematological analysis, the levels of glucose and cholesterol in the blood were decreased slightly in the males and females rats at doses of 0.008 or 1 g/kg. At the all dose groups, there were no significant changes in the body weights, but autopsy findings of all organs showed reduced weights in the thymus of males in the high dose groups of 1 g/kg and 5 g/kg. These results indicate that P. sinclairii does not induce any significant toxic effect on Sprague-Dawley rats treated for 2 weeks, but the reduced weights of thymus in males may require a further long-term investigation.