Purpose: The purpose of this study was to investigate the influence of implant and drill diameters on the stability of implant and bone response. Materials and Methods: An implant (GS II, Osstem Implant) with a 3.5-mm diameter and drills with three different diameters, differentiating the volume of bone compacted by the implant, were used in this study. Measurement of the insertion torque and observation of bone compression patterns were done during implant site preparation in minipigs. Also, analysis of resonance frequency, histomorphology, marginal bone resorption, and new bone formation were performed. Results: Microstrains and microcracks occurred in cortical bone around the thread when a drill with a smaller diameter than that of the thread was used. Higher implant stability was shown and maintained when a small-diameter drill was used. When using a drill with a smaller diameter than the root diameter of the implant thread, the bone-to-implant contact/bone area (BIC/BA) was higher than the wider drill during the whole test period. However, the use of a wide drill was the most rapid in increasing the BIC/BA value by new bone formation. In the cancellous bone, the speed of new bone formation was not different in each test group. However, the formation of new bone was faster when a large-diameter drill was used in the cortical bone. There was no significant difference in marginal bone loss (MBL) according to drill diameters, but the speed of MBL was fast when using a drill that was smaller than the root diameter of the implant thread. Conclusion: Implant stability, BIC, and BA were high when using a final drill that was smaller than the root diameter of the implant thread compared with a wide final drill. However, the speed of new bone formation was relatively slow and the speed of MBL was relatively fast if the final drill was excessively smaller. Keywords: bone response, dental implant, implant stability, osteotomy preparation size