Objective To investigate the effects of ovariectomy on genioglossus（GG） electromyography and myofibre phenotype in female rats and to explore the proposal mechanisms underling ovarian hormone protecting to the patency of upper airway（UA）. Methods 30 female Sprague- Dawley rats were randomly assigned to three groups: normal group（NORMAL）, sham group（SHAM） and ovariectomized group（OVX）. Six weeks later, electromyography activity of the genioglossus（EMGgg）was obtained from inserted bipolar electrodes. The integrated EMG（iEMG）was analyed. Genioglossus was stained with ATPase staining. The fibre phenotype composition and cross sectional area （CSA）of type ⅡA and ⅡB/ⅡX fibres were measured. Results EMGgg had no significant variety between the normal and sham group（P>0.05）. Compared to normal group, iEMG was significantly decreased in OVX group（P0.05）, but the CSA of type ⅡA was significantly decreased（P
