A great geomagnetic storm occurred around 1640 UT on April 6, 2000, with a Value of -317nT in Dst index. The responses of the ionosphere at Wuhan during the first stage of this storm were reported in this paper. Soon after the sudden storm commencement (SSC) at 1640 UT, the main phase of the geomagnetic storm appeared, and the storm stepped into its recovery phase at the beginning of the next day. A rapid and large increase in the ionospheric heights at Wuhan occurred at the beginning of the main phase, and the lifts in h'F and h
mF
2 lasted for about 2 hours. The value of f
0F
2 decreased about 1.6 MHz at the beginning of the main phase, and the maximum value of f
0F
2 on the next day was less than that on April 5 more than 3 MHz at Wuhan. The almost simultaneous increase in h'F was also observed at Chungli, Taiwan. The near simultaneity of the h'F disturbances at the two stations suggested that an E x B plasma drift due to an east-west electric field of storm origin was the cause of the rapid and large lifts in the nighttime ionospheric heights after the SSC.