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In order to evaluate drought tolerance of some Aegilops triuncialis ecotypes a factorial experiment based on a completely randomized design was conducted under non-stress and drought stress (irrigation until 50% of heading) condition in the greenhouse of Mohaghegh Ardabili University in 2012. Drought tolerance and susceptibility indices for grain yield were calculated and principal component analysis was performed based on these indices. The results showed that based on the stress susceptibility index (SSI) and stress tolerance index (TOL) Horand and Karaj ecotypes are less sensitive to water stress. In terms of stress tolerance index (STI) and geometric mean productivity index (GMP) which a high values of them indicates tolerance of studied ecotypes، Hashtrood ecotype were identified as a tolerant ecotype. Grouping of ecotypes in a three dimensional graph based on the yield the in non-stress (Yp)، yield the in stress condition (Ys) and stress tolerance index (STI)، showed that Maku and Hashtrood ecotypes under both non-stress and drought stress conditions، and Horand ecotype under stress condition have higher performance. With Principal components analysis and biplot diagram، Hashtrood، Maku and Horand ecotypes were identified as drought tolerant. According to significant correlation between STI، GMP، MSTI1 and MSTI2 indices with yield under stress and non-stress conditions، these indices can be used for determination of tolerant ecotypes.