AbstractTannin-formaldehyde resins (TFR) were prepared by copolycondensation of tannins (larch tannin or valonia tannin) and formaldehyde. The performances of TFR and the free formaldehyde residue in the system during the course of reaction were tested. Chemical and structural changes of TFR during the reaction process were detected by Fourier transform infrared spectroscopy (FTIR) and 13C nuclear magnetic resonance spectroscopy (13C NMR). The results indicated that larch tannin-formaldehyde (LTF) resins demonstrated higher viscosity, higher solids content, shorter gel time, and lower free formaldehyde content than valonia tannin-formaldehyde (VTF) resins. The FTIR and 13C NMR tests demonstrated that larch tannin had higher reactivity than valonia tannin with formaldehyde, which was confirmed by the results of the free formaldehyde content measurement and the characteristics of TFR.