Abstarct: Drought is one of the most important factors which limiting crop growth and production in arid and semiarid regions of the world. In sustainable agriculture using of biological fertilizers such as soil bacteria is one of the novel solutions for reduces environmental damage caused by environmental stress. In order to evaluate influence of Pseudomonas fluorescens on some morphological and physiological characteristics of potato under water deficit stress, an experiment was conducted as split-plot factorial baxsed on randomized complete block design with three replicates in the farm of Shahrood University of Technology. Three deficit irrigation were assigned as a major factor (7, 10 and 14 days irrigation periods) and Pseudomonas bacteria (inoculated and non inoculated) as the first sub-factor and two varieties (Savalan and Agria) as the second sub-factor. Before planting, potato tubers were inoculated with Pseudomonas fluorescens bacteria (concentration of inoculants 108 cells per g of bacteria) and after planting plants were irrigated uniformly in all treatments. After 58 days deficit stress were applied to deficit treatments. The results showed that deficit stress were able to decrease bulb diameter, harvest index, biological and economic yeild, tuber protein, chlorophyll content and relative water content, while traits such as plant and soil phosphorus, leaf potassium percentage and proline content were increased. In inoculated treatments biological yield was improved and in compare to control, yield has increased 22.86% when inoculated with Pseudomonas while percentage of membrane damage was decreased.The inoculation with bacteria had beneficial effects on the membrane damage, morphological and physiological characteristics of plants under water deficit conditions.