Purpose: The present study was conducted to investigate, clinically and radiographically, the effect of two different designs of Extracoronal precision attachments on the abutment teeth and supporting structures in unmodified Kennedy class II mandibular cases treated with removable partial denture. Material and methods: For each patient, The lower first and the second premolars on the experimental side were prepared to receive two porcelain veneered crowns with the Extracoronal attachment. patients were divided into two groups, each of seven patients. Group (1) Patients were treated with conventional removable partial denture retained by ball and socket extra-coronal precision attachment (OT CAP attachment). Group (2) Patients were treated with unilateral (side plate) removable partial denture retained by anther design of extra-coronal precision attachment (OT unilateral). Evaluation was carried out clinically by measuring the probing depth using Williams graduated periodontal probe, and radiographically using the Digora computerized system. at the time of prosthesis insertion , 6 months, 12 months and 18 months. Results: Results revealed that, regarding the bone height, there was no statistically significant difference between % of bone loss in the two groups after 6 months as well as after 12 months. After 18 months. Group I showed statistically significantly higher mean % of bone loss than Group II .regarding the bone density, Through all periods; Group II showed statistically significantly higher mean % increase in bone density than Group I which showed a decrease in bone density. Through all periods; there was no statistically significant difference between mean % increase in PD of the two groups.