Background : Inhaled glucocorticoids are the medical treatment of choice in asthma patients. Fluticasone propionate is one of the most effective inhaled corticosteroids and has been reported to have minimal effect on the hypothalamic-pituitary-adrenal axis at the recommended dose. However, reports of long-term trials characterizing their systemic safety with chronic use are rare. This study was designed to evaluate the long-term safety of inhaled fluticasone propionate to the hypothalamic-pituitary-adrenal axis. Method : This study was conducted on 21 patients to evaluate the adrenal response to rapid ACTH stimulation test after 6 months of treatment with fluticasone propionate from $200;{mu}g$ to $750;{mu}g$ daily. The serum cortisol levels was measured to assess its effect on the hypothalamic-pituitary-adrenal axis just prior to the injection, at 30 minutes and 60 minutes after an intramuscular injection of synthetic ACTH. Result : The mean dose of inhaled fluticasone propionate was $355;{mu}g$ per day(SD=$174;{mu}g$, range=$200;{mu}g$ to $750;{mu}g$). The mean serum cortisol levels of the patients was $11.0;{mu}g/d{ell}$(SD=$6.4;{mu}g/d{ell}$) prior to the injection, $20.0;{mu}g/d{ell}$ (SD=$7.7;{mu}g/d{ell}$) after 30 minutes, and $23.0;{mu}g/d{ell}$(SD=$6.3;{mu}g/d{ell}$) after 60 minutes. Sixteen patients of the 21 patients had a normal response(> $18;{mu}g/d{ell}$), and 5 out of the 21 patients had serum cortisol levels below the normal range after the rapid ACTH stimulation test. Conclusion: Adrenal suppression occurred in 5 out of 21 patients with 6 months treatment with inhaled fluticasone propionate.