The degree of retention for overdenture attachments depends on design, location, and alignment of supporting dental implants and the type of attachments. The aim of this study was to evaluate the retention of an implant-supported overdenture with different attachment designs. An overdenture was made on an edentulous mandibular model with 2 ITI implants (4.1 × 10 mm) in the symphyseal region. Five specimens of 8 attachment designs with corresponding abutments and superstructures were used: ITI regular Dolder bar with 1 metal clip, ITI regular Dolder bar with cantilever and 3 metal clips, Hader bar with 1 plastic clip, Hader bar with cantilever and 3 plastic clips, Sphero block abutment with Rhein plastic caps (green, white, and pink), and retentive anchor with ITI elliptical matrix. The attachments' housings were interchangeable and fixed into the overdenture through nut and screw. The overdenture attachments were subjected to 8 consecutive pulls on a universal testing machine with a crosshead speed of 50.8 mm/min in the vertical and posteroanterior directions. Analysis of variance and Duncan tests were used to determine differences between mean retention values (α = .05). The highest average value retention was recorded for the ITI Dolder bar with cantilever and 3 metal clips in both the vertical and posteroanterior directions, respectively (P < .05). The Rhein pink caps had the lowest retention in the posteroanterior direction (P < .05). Retention decreased over the course of consecutive pulls for all attachments in both directions. The type, number, and placement of attachments affect the retention of implant-supported mandibular overdentures.