Aim of study: was to evaluate patient's satisfaction and stress distribution of flexible versus Cobalt-chromium (Co-Cr) denture base material in Kennedy class I partially edentulous patients. Materials and methods: Eight partially edentulous patients with ages ranged from 45-55 years. All patients had mandibular Kennedy class I classification with the second premolars as last standing abutment teeth;Patients were divided into two groups, (Group I)four patients received Co-Cr lower removable partial denture and use it for 3 months then received flexible lower removable partial denture and(Group II).Another four patients received flexible lower removable partial denture and used it for 3months, then received Co-Cr lower removable partial denture.Stress on the two second premolar natural teeth abutments and patient satisfaction were evaluated for group I and group II after each three months of delivery of each dentures. Results:The results of this study showed that there were significant increases in satisfaction level for assessed variables (general satisfaction, aesthetics, mastication, comfort and retention) of the patients after wearing flexible acrylic resin denture base than they wearingCo-Crremovable partial denture recorded statistically significant higher strain mean value than flexible group .Conclusion: Patient satisfaction for wearing flexible partial denture was higher than that for those wearing Co-Cr partial denture. The flexible lower removable partial denture is much better to decrease the applied load on the abutment than Co-Cr partial denture