We performed a 90-day repeated-dose inhalation toxicity study of soluble hexavalent chromium trioxide (CrO3 (VI)). Male Sprague-Dawley (SD) rats were exposed to doses of CrO3 in the form of 0.5˜5.0 μm aerosol at 0.00, 0.20, 0.50, and 1.25 mg/m3 for 6 h/day, 5 days/week for 13 weeks using inhalation chamber. CrO3 induced decrease of activity, alopecia and nasal hemorrhage. Body weights of the high-dose 1.25-mg/m3 exposure group were significantly lower than those of the control group. Hematological results revealed the reduction of the number of red blood cell and hematocrit values in the 1.25-mg/m3 exposure group. In addition, the hemoglobin values in the 0.50- and 1.25-mg/m3 exposure groups were significantly decreased compared with those of the control group. Clinical biochemical measurements revealed the reduction in total protein, albumin and alanine aminotransferase (ALT) level of the 0.50- and 1.25-mg/m3 exposure groups. Microscopic examination of the lung showed inflammation reactions caused by Cr exposure. In conclusion, the 13-week repeated exposure with soluble CrO3 demonstrated the injury in SD rats with the no observed adverse effect level (NOAEL) under 0.20 mg/m3.