A field experiment was conducted at Regional agricultural research Station, Tirupati during kharif 2010 with15 groundnut prerelease and released groundnut genotypes. Thermo tolerance of these genotypes across the important growth phenophases were measured using reliable traits viz., Relative injury to the cell membranes and Chlorophyll fluorescence ratio (Fv/Fm) of photosystem II. The results clearly indicate that groundnut is susceptible to high cellular damage due to high temperature stress at pod maturity stage compared to the flowering and pegging stages. The genotypes TCGS-991 recorded low mean membrane injury (10.08%), high chloroplast activity (0.540) with highest pod yield of 2037.8 Kg/ha followed by TCGS 969, TCGS 1043. These entries possess high potential to maintain themostabilty under high temperature conditions and also produced higher pod yield. Among the other entries, Greeshma and TCGS-894 recorded highest thermo stability of cellular membranes and chloroplast activity with moderate yields. These genotypes can be recommended to high temperature conditions or may be used as potential donor source in resistance breeding programs for developing varieties in pursuit of global warming.