Wild barley contains a wide genetic diversity and therefore is adaptable to all kinds of harsh environments. The aim of this research was to determine the extent of drought stress adaptation within Hordeum spontaneum L. genotypes from different climates of Iran. From the primary population of 193 genotypes, a core set consisting of 18 genotypes, were selected based on the highest squared Euclidean distance to represent the genetic diversity among wild barley genotypes. The selected genotypes were evaluated for drought stress adaptation. At the beginning of flowering time, two different water treatments; well-watered (90-100% field capacity) and drought stress (20-30% field capacity) were imposed to the plants. A negative correlation of stress tolerance index with phenological traits and relative water loss was observed. Genotypes with the highest relative water loss under drought stress condition were mainly from Mediterranean and Cool steppe climates and genotypes from desert climates seemed to have better adaptability to drought stress shown by less relative water loss. It seems that genotypes from unpredictable climatic conditions are more adapted to harsh environments.