Abstract: The influence of cold air from middle latitude in Southern Hemisphere on tropical weather systems and the response of the latter were studied using lower tropospheric data May and June, 1974-1983. The results showed that there were about three cold air invasions from around 31 °S onto the tropics per month and the time reguisite for each invasion was 24 to 48 hours in most cases. The responses in low latitudes could be various according to different intensity and speed of cold air invading.