In this study, the effect of whole body irradiation (WBI) with different low doses of X-rays on the expression of Glucocorticoid receptor (GCR) in mouse splenocytes and the time course of GCR expression after WBI with 75mGy X-rays were observed using the radioactive ligand binding assay. Results showed that the GCR expression in mouse splenocytes decreased significantly 8h after WBI with 25, 50 and 75mGy X-ray irradiation, and in the case of 75mGy, the GCR expression began to decrease 4h after irradiation. Based on the fact that WBI with low doses of X-rays could reduce GCR expression in mouse splenocytes, it suggested that the down-regulated GCR expression may play a role in the enhancement of immune effect caused by low dose radiation.