BACKGROUND: This study investigated anti-inflammatory effects of exosomes derived from human fetal cartilage progenitor cells (hFCPC-Exo) and their microRNAs (miRNAs) on the osteoarthritis (OA) phenotype in vitro in comparison with exosomes from bone marrow mesenchymal stem cells (MSC-Exo). METHODS: SW982 cells (synoviocytes) or hFCPCs (chondrocytes) were stimulated with 10 ng/mL IL-1β to mimic OA phenotypes. The effects of hFCPC-Exo and MSC-Exo were compared by measuring the expression of inflammatory cytokines and an anti-inflammatory protein. miRNA profiles of hFCPC-Exo and MSC-Exo were analyzed using a 2588 human miRNA dataset, and miRNAs potentially involved in the anti-inflammatory effect of hFCPC-Exo were selected. miRNA mimics and antisense inhibitors were used to investigate the role of selected miRNAs in the IL-1β signaling pathways. RESULTS: Both hFCPC-Exo and MSC-Exo significantly decreased the expression of inflammatory cytokines (IL-1β, IL-6, and MCP-1), while slightly increased an anti-inflammatory protein (SOCS1) in IL-1β-treated SW982 cells. miRNA sequencing revealed anti-inflammatory miRNAs present in large amounts in both hFCPC-Exo and MSC-Exo. Among them, miR-125b-5p mimic significantly suppressed the expression of inflammatory cytokines induced by IL-1β, while anti-sense inhibitor of miR-125b-5p efficiently blocked anti-inflammatory effects of hFCPC-Exo. Both hFCPC-Exo and miR-125b-5p inhibited IκBα down-regulation and -NF-κB stabilization in IL-1β-treated SW982 cells. Additionally, hFCPC-Exo and miR-125b-5p showed similar effects on IL-1β-treated hFCPCs as an OA model in chondrocytes by down-regulating the expression of IL-1β, MMP13, and ADAMTS-5 and up-regulating the expression of aggrecan (ACAN) and type II collagen (COL2A1). CONCLUSION: This study demonstrated that hFCPC-Exo exhibits anti-inflammatory effects on IL-1β-treated synoviocytes and chondrocytes in vitro possibly by down-regulating the IL-1β-TRAF6-NF-κB pathway via anti-inflammatory miRNAs such as miR-125b-5p.