Objective: To study the regulative effects of Aspergillus fumigatus (A.fumigatus) on expression of glucocorticoid receptor (GCR) in asthmatic rats. Methods: Wistar rats were randomly divided into 4 groups: a normal control group (UC), a normal control with A. fumigatus group (UC+ AF), an OVA group (OVA), and an OVA with A. fumigatus group (OVA+ AF). OVA and OVA+ AF groups were sensitized and challenged with OVA to establish asthmatic models. UC and UC+ AF groups were given normal saline as controls. After the last challenge, OVA+ AF and UC+ AF groups were given A. fumigatus spores intranasally. Airway hyper-responsiveness, eosinophil percentage (Eos%) and serum IgE level were measured to confirm the establishment of asthmatic models. Sections of pulmonary tissue were stained with hematoxylin-eosin (HE) and the expression of GCR mRNA and protein in lung tissues were measured by qRT-PCR and Western blot. Lung tissues and blood were plated on the potato dextrose agar(PDA)medium and cultured for 24 h to measure the number of colony. Results: The Penh value, Eos% in BALF and serum IgE level in UC+ AF group were slightly higher than those in the UC group (all the P>0.05). The Penh value, Eos% in BALF and serum IgE level in OVA group were significantly higher than those in the UC group (all the P<0.05). The Penh value in OVA+ AF group was significantly increased compared with the OVA group at the concentration of 25 g/L and 50 g/L of methacholine (all the P>0.05). Pulmonary histology revealed that both OVA group and OVA+ AF group showed high levels of inflammatory cell infiltration of bronchus and lung vessels, interstitial edema and smooth muscle thickening, while the UC and UC + AF groups were normal. Compared with the UC group, the expressions of GCR mRNA and protein in UC+ AF group and OVA group were decreased significantly (GCR mRNA in UC, UC+ AF and OVA group were 0.93±0.15, 0.65±0.10, 0.72±0.22, respectively, F=10.744, P<0.01; GCR protein in UC, UC+ AF and OVA group were 100±0, 89±8, 82±15, respectively, F=18.939, P<0.01). The expressions of GCR mRNA and protein in OVA+ AF group were further decreased than those in OVA group (GCR mRNA: OVA group: 0.72±0.22 vs OVA+ AF group: 0.52±0.08, t=2.462, P<0.05; GCR protein: OVA group: 81.88±15.41 vs OVA+ AF group: 59.09±7.60, t=2.997, P<0.05). The ratio of A. fumigatus colonization in lung tissues in OVA+ AF group (4/8) was higher than the UC+ AF group (0/8). Conclusion:A. fumigatus exposure can down-regulate the expression of GCR in the lung, which maybe an important mechanism of steroid-resistant asthma.