Objectives To systematically review and provide estimates of the minimal important change (MIC) and difference (MID) for outcome tools in people with knee osteoarthritis (OA) after non-surgical interventions. Design A systematic review. Data sources MEDLINE, CINAHL, Web of Science, Scopus and Cochrane databases were searched up to 21 September 2021. Eligibility criteria We included studies that calculated MIC and MID using any calculation method including anchor, consensus and distribution methods, for any knee OA outcome tool after non-surgical interventions. Data extraction and synthesis We extracted reported MIC, MID and minimum detectable change (MDC) estimates. We used quality assessment tools appropriate to the studies' methods to screen out low-quality studies. Values were combined to produce a median and range, for each method. Results Forty-eight studies were eligible (anchor-k=12, consensus-k=1 and distribution-k=35). MIC values for 13 outcome tools including Knee injury and Osteoarthritis Outcome Score (KOOS)-pain, activities of daily living (ADL), quality of life (QOL) and Western Ontario and McMaster Universities Arthritis Index (WOMAC)-function were estimated using 5 high-quality anchor studies. MID values for 23 tools including KOOS-pain, ADL, QOL and WOMAC-function, stiffness and total were estimated using 6 high-quality anchor studies. One moderate quality consensus study reported MIC for pain, function and global assessment. MDC values from distribution method estimates for 126 tools including KOOS-QOL and WOMAC-total were estimated using 38 good-to-fair-quality studies. Conclusion Median MIC, MID and MDC estimates were reported for outcome tools in people with knee OA after non-surgical interventions. The results of this review clarify the current understanding of MIC, MID and MDC in the knee OA population. However, some estimates suggest considerable heterogeneity and require careful interpretation. PROSPERO registration number CRD42020215952.