This study investigated the improved properties of calcium carbonate (CaCO 3 ) modified urea-formaldehyde (UF) resin adhesive for medium density fiberboard (MDF) production. The CaCO 3 modified UF resins were prepared by adding different proportions of CaCO 3 to a low molar ratio UF resin at the initial stage of a typical synthetic process of the resin. The physicochemical properties of the resins were measured. The mechanical and environmental performances of the resin-bonded MDF panels were tested. The results show that the viscosity and free formaldehyde content of UF resins with or without CaCO 3 modification were not significantly different. The solid content of the CaCO 3 modified UF resin was significantly lower than that of the control group. In addition, the measured gel time of the CaCO 3 modified UF resin was 111-149 s, which was longer than that of the control resin (82 s). The gel time was further extended with the increase of the CaCO 3 content in the UF resin. The chemical group and crystal structure of UF resins with or without the modification of CaCO 3 were not significantly different. The internal bonding (IB) strength of the MDF panels significantly increased from 0.75 MPa to 0.97 MPa when the UF resin was modified with 2% of CaCO 3 . This study provides scientific support for the preparation of inorganic mineral modified UF resins for strength enhanced wood-based panel manufacturing.