Drought stress is a major abiotic stress of common bean(Phaseolus vulgaris L.) throughout the world. Increasing the proline accumulation contributes to enhance crop drought tolerance. A c DNA for δ-o rnithine aminotransferase(δ-OAT), an enzyme involved in the biosynthesis of proline, was isolated from Phaseolus vulgaris(Pv OAT). Pv OAT exhibits 87.4 and 39.8% similarity of the deduced amino acid sequences with δ-OAT from Glycine max and Vigna aconitifolia, respectively. The transcriptional analysis revealed that Pv OAT was strongly induced by drought stress. And the expression of Pv OAT was higher in leaves than that in the root and stem of common bean by drought stress. Similar increase of the proline accumulation was observed in leaves and roots of common bean by drought stress. Furthermore, the proline content, the Pv OAT expression and the Pv OAT enzyme activity in cul tivar F5575 was significantly(P<0.01) higher than that in cultivar F4851 under drought-stress conditions. Interestingly, it had been observed that, in the later stage of drought stress, the proline steadily maintained at the maximum level maybe result from the Pv OAT enzyme activity increasing steadily. These r esults indicated that the expression of Pv OAT and the accumulation of proline induced by drought stress treatment were related to the degree of common bean drought tolerance. So our results support the view that δ-OAT is associated with proline synthesis under drought stress conditions. Increasing the proline accumulation contributes to enhance crop drought tolerance. A c DNA for δ-o rnithine aminotransferase (δ-OAT), an enzyme involved in the biosynthesis of proline, was isolated from Phaseolus vulgaris (Pv OAT). Pv OAT exhibits 87.4 and 39.8% similarity of the deduced amino acid sequences with δ-OAT from Glycine max and Vigna aconitifolia, respectively. The transcriptional analysis revealed that Pv OAT was strongly induced by drought stress. And the expression of Pv OAT was higher in leaves than that in the root and stem of common bean by drought stress. Similar increase of proline accumulation was observed in leaves and roots of common bean by drought stress. , the proline content, the Pv OAT expression and the Pv OAT enzyme activity in cul tivar F5575 was significantly (P <0.01) higher than that in cultivar F4851 under drought-stress conditions. Inter estingly, it had been observed that, in the later stage of drought stress, the proline steadily maintained at the maximum level maybe result from the Pv OAT enzyme activity increased steadily. These r esults indicated that the expression of Pv OAT and the accumulation of proline induced by drought stress treatment were related to the degree of common bean drought tolerance. So our results support the view that δ-OAT is associated with proline synthesis under drought stress conditions.