Purpose: The aim of this investigation was to compare the chewing efficiency after immediate and delayed loading of mini-implants that served as supplementary support for removable partial dentures (RPDs). Materials and Methods: In this four-center randomized trial, patients who had RPDs in arches with unfavorable tooth distributions, ie, no canine and at most two posterior teeth in one or both quadrants, received strategic mini-implants with ball abutments. The mini-implants in group A were loaded immediately either by housings with O-rings (insertion torque ≥ 35 Ncm) or by soft relining material (insertion torque 35 Ncm). In group B, the RPDs were only hollowed over the balls. After 4 months, the soft relined RPDs and all RPDs of group B received the housings. Masticatory efficiency was evaluated with a validated mixing ability test of two-colored chewing gum before surgery and 14 days, 4 months (before housing pickup), 4.5 months, and 12 months after surgery. The circular variance of hue was the measure of mixing. Results: From 76 participants with 79 RPDs, 38 each were randomly allocated to group A or B. In group A, the housings in six participants were picked up immediately, and the remaining RPDs were primarily soft relined. There was a significant group difference only after 4 months. The mixing ability was better after immediate loading than after delayed loading (P .0001). In group B, the chewing efficiency was notably deteriorated after the RPDs were hollowed over the ball abutments. However, immediately after all housings were picked up, the chewing efficiency in both groups was substantially improved, and the variance of hue values after 1 year were very similar in the groups. Conclusion: The chewing performance can be improved by inserting supplementary mini-implants under existing RPDs with unfavorable tooth support. This improvement occurred faster by immediate loading than by delayed loading. Keywords: chewing function, dental, mini-implant, randomized controlled clinical trial, removable partial denture, strategic