Abstract: During a medium magnetic storm on 5 April 2006, ionospheric plasma bubbles have been studied in a large area using data from the Global Positioning System (GPS) observation sites between 70ºE and 210ºE in longitude, 20ºS and 40ºN in latitude. The plasma bubbles were found between 160ºE~90ºE, and 12ºS~33ºN, appeared at about 1~1.5 hour after local sunset. The plasma bubbles occurred earlier and survived longer in the southern hemisphere than those in the northern hemisphere. And in the development process of the plasma bubbles, at about 1100 km the upward drift speed was about 300 m/s mapped onto the magnetic equator. The plasma bubbles tilted during the development. The existence of the eastward electric field was supposed to be the cause triggering the plasma bubbles.