Urea-formaldehyde (UF) resins based on different formaldehyde/urea (F/U) mole ratio were synthesized with oxidized cassava starch added at the final stage of the resin synthesis process. The basic characteristics of resins including solid content, viscosity, and curing time were studied, and the dry and wet bond strengths were evaluated by producing a three layer plywood. Additionally, the curing characteristics of different resins were investigated via differential scanning calorimetry (DSC). Structural distributions between UF and oxidized cassava starch were examined via FT-IR and 13C NMR analysis. The results indicated that the addition of oxidized starch not only improved resin bond strength but also notably reduced the curing start temperature of modified resins. Furthermore, a negative relationship between F/U mole ratio and the extent of reduction was identified. The structural distribution of UF resins changed dramatically because of oxidation cassava starch addition, but the changes varied due to different F/U mole ratios.