Aim: Radiographically evaluate the alveolar bone height change of the abutment crystal alveolar bone and residual alveolar ridge by using three different modalities for long span distal extension bases. Materials and methods: In a randomized controlled clinical trial, fifteen patients with completely edentulous maxilla and remaining mandibular six anteriors and 1st premolar.  They were randomly divided to three groups. All patients received maxillary complete denture. Group A patients  provided with flexible denture base removable partial denture (RPD), Group B patients provided with resilient layer RPD and group C patients provided with occlusal reactive RPD. The abutment teeth was evaluated radiographically by digital periapical radiographs after insertion, after 6 months and after 12months. The mandibular residual alveolar ridge was evaluated by digital panoramic radiograph.   Results: Group A (Flexible denture base RPD) significant increase in bone resorption of both abutment and mandibular residual alveolar ridge compared to those in Group B (Resilient layer denture) and Group C (Occlusal reactive denture). Conclusion:From the point of view of resorption of abutment bone height and residual alveolar ridge bone height, the flexible denture base causes more bone resorption in mandibular distal extension  removable  partial denture (DERPD)  than  Resilient layer denture base  and  Occlusal reactive denture base. So, Resilient layer denture base and Occlusal reactive denture base more reliable in management of (DERPD) than Flexible denture base. Key words: mandibular, Flexible, Soft liner, Resilient layer denture, Occlusal reactive.