Six sounding rockets, each carrying a Langmuir probe and an impedance probe, were launched into the disturbed ionosphere Syowa Station, Antarctica, during 1972--1973 for measuring electron density fluctuations in a frequency range from a few hertz to 160 Hz. Such low-frequency fluctuations were observed between 90 and 120 km in altitude and found to have relative amplitudes of 10% or smaller. Analysis to find the frequency power spectrum of the fluctuations shows that in most cases the spectral form obeys f-1~f-3. in this report we wish to summarize the measured characteristics of the fluctuations and briefly discuss possible generation mechanisms of them.