BACKGROUND: The minimal clinically important differences (MID) of the Oral Health-related Quality of Life (OHRQoL) are the benchmark to meaningfully interpret treatment outcomes. However, there is no available information regarding the factors impact the MID variations after removable partial denture (RPD) treatment. OBJECTIVE: The purpose of this study was to determine the influence of the pre-treatment OHRQoL impairment on the MID in the oral health impact profile (OHIP) after RPD treatment. METHODS: In this prospective study, OHIP and Self-reported Oral Health (SROH) questionnaires were administered to patients before and 3 months after RPD treatment. The MID in each OHIP version (OHIP-49, OHIP-20, OHIP-14 and OHIP-5) was the mean score of patients who showed a minimum SROH improvement. Multiple linear regression analysis was conducted to determine the influence of the pre-treatment OHIP summary score on the MID score. RESULTS: Among 248 participants who completed both evaluations, 85 (34%) patients had minimum SROH improvements after RPD treatment. Multiple regression analysis indicated that each 10-point increase in the pre-treatment summary OHIP score was associated with an increase in the MID score of three points for OHIP-49 and four points for OHIP-20, OHIP-14 and OHIP-5 (P < .05), after controlling for age, sex and the number of missing teeth. Therefore, the MID increased as the pre-treatment OHRQoL was impaired. CONCLUSIONS: The MID was accounted for by approximately one-third of the pre-treatment summary score, independent of the OHIP version, in the interpretation of the effects of RPD treatment on patients' OHRQoL.