The objective of this study was to evaluate the retentive force of one-piece implant (Nobel Direct; Nobel Biocare, Sweden) -supported overdentures including a telescope system. The regular platform Nobel Direct (4.3 mm dia.) was embedded in a brass patrix frame (10 x 10 x 25 mm) using autopolymerized polymethyl methacrylate (PMMA; Unifast II, GC). Two sizes of O-rings [O1 (2.8 mm dia.) and O2 (3.8 mm dia.), SAN-EI, Japan] and protection caps (PC; Straumann) were placed on the Nobel Direct abutment head. The plastic patterns of the Konus telescope outer crown were fabricated on the Nobel Direct abutment head and cast using the GC autocast system. As a control, the PMMA resin (RE) was made to directly touch the abutment head. The patrix and matrix frames were connected under 2 kg and then mounted on a screw-driven mechanical testing machine (Model UTM II, Toyo Boldwin, Japan). The retentive force (n=5, N) obtained at a crosshead speed of 40 mm⁄min was analyzed by ANOVA⁄Scheffe's test (α=0.05). The larger O-ring had less retentive force than the smaller O-ring. The Konus telescope had a retentive force comparable to that of the smaller O-ring (p>0.05). Although the retentive forces of the Konus telescope tended to increase as the connecting load increased, the force of the O-ring did not vary according to the connecting loads. For the one implant-supported overdentures, not only a medium-sized O-ring and protection cap but also coping and Konus telescopes demonstrated having appropriate retentive force.