ALIMOV - Astrophysical institute of the Tajik Academy of Sciences, Dushanbe,۷۳۴۰۴۲,Buchoro str.۲۲, Tajikistan
V. BLOKHIN - Astrophysical institute of the Tajik Academy of Sciences, Dushanbe,۷۳۴۰۴۲,Buchoro str.۲۲, Tajikistan
NEGMATULLAEV - Institute of Seismic Resistant Construction and Seismology of the Tajik Academy of Sciences, Dushanbe, ۷۳۴۰۲۹,Aini str.۱۲۱, Tajikistan.

An analysis of the ionospheric effects during the Gissar and Gindukush earthquakes 23.01.89 and 31.01.91 was made on the basis of data of vertical sounding of the ionosphere at Dushanbe station. The F2 layer critical frequences and Ym = hpF2 – hF was used for it. The investigations of ionospheric data shoved that the value of foF2 increases and Ym descreases , and also intensification of F- spread over the heightand were observed 2-3 days before an earthquake.