Purpose: The aim of this study was to compare between the effects of using two different designs of extra coronal precision attachments on supporting structures of the abutment teeth in unilateral free end saddle partial denture. Material and Methods: Ten Kennedy class II partially edentulous patients with the last second premolar which is lasting abutment tooth were selected. The patients were divided into two groups (each group five patients), group I; patients were received unilateral partial denture retained by OT unilateral extra coronal attachment, group II; patients were received partial denture retained by OT cap extra coronal attachment with bilateral cross arch stabilization. Clinical evaluation including pocket depth measurements at four sides of last abutment tooth and radiographic evaluation using cone beam computed tomography (CBCT) was done at time of partial denture delivery, after 6, 9 and 12 months. Results: Inspection of radiographic evaluation revealed non-statistical significant difference between the two groups at the time of insertion, 6 and 9 months while after 12 months group II showed more bone loss than group I. Regarding the clinical evaluation showed non-statistical significant difference in pocket depth between two groups at time of insertion, 6 and 9 months and more pocket depth in group II at 12 months. Conclusions: Using special design of extra coronal castable precision attachment (OT unilateral) exerts less stresses on the abutments and their supporting structures in comparison with OT cap attachment, in addition to it is simple and more comfortable to the patients.