Abstract: The factors of influencing interal-bonding strength when using urea-formaldehyde resin adhesives (UFRA) synthesized in strong acid were studied with single factor tests, viscosity characteristics analysis and vapour pressure osmometer measuring. The optimal technological procedure for synthesizing UFRA in strong acid to get enhanced bond strength was worked out. It was found that strength-bond was closely related to the molar ratio between formaldehyde and urea in technology. The bond strength was improved and average molar quality rose when the molar ratio ( n F/ n U 1 ) between formaldehyde (F) to first-urea (U 1) was decreased. The UFRA was made so that bond strength was up to 1 19 MPa and free formaldehyde content was only 0 09% when n F/ n U 1 was 2 6, the molar ratio ( n F/ n U 2 ) between formaldehyde and urea (U 2)(added urea in strong acid and weak base) 1.5 and the molar ratio between formaldehyde and urea (total urea) 1.2.