Abstract: The effect of impregnated papers with different molar ratios(F/U)of UF on physical mechanical strength and formaldehyde emission of surface decorated wood-based panels was discussed. At the same time, the impregnated papers were pressed and pasted onto the tinfoil, then, formaldehyde emission of impregnated papers was tested, and the formaldehyde source of surface decorated wood-based panels was analysed.The results showed that the physical mechanical strength and formaldehyde emission of surface decorated wood-based panels increased according to molar ratio. The paper with impregnated thermosetting resins with good ability of sealing formaldehyde can seal most formaldehyde from panels. The formaldehyde emission from impregnated papers accounted for 56% of that from surface decorated wood-based panels when molar ratio was 1.55. It could reduce the formaldehyde emission effectively by reducing molar ratio of UF for impregnated papers. The formaldehyde emission of surface decorated wood-based panels was much less than the E₁ national limit standard when molar ratio was 1.4.