Abstract: Using the historical data from ionosonde stations and satellite, the response of ionospheric f0F2 to major Interplanetary magnetic Field (IMF) southward turnings in mid- and low-latitudes is studied. It shows that the IMF southward turnings can cause disturbing response in the ionosphere, which depends on latitude, season and local time when the turning occurs. In mid-latitude, the ionospheric response to southward turnings in summer and equinox and by night is stronger, which fades out with latitude decreases. During the recovery phase the irregular fluctuation in the ionosphere comes forth. In low-latitude, the disturbance caused by the turnings is strong in summer and equinox and weak in winter, although it tends to be immersing into the background disturbances. It is also found that the maximal negative responses of the ionosphere is well related with the maximal negative Bz after the southward turnings linearly.