To investigate the color darkening effects that low molecular weight phenolformaldehyde(PF)resin may produce, UV and IR were used to analyze light absorption of main products during synthesizing and solidifying of the resin. Resin synthesis and wood sample treatment conditions were determined and color difference of treated Populus ussuriensis samples with the resin were measured. The results showed that color difference of both the treated and the control was small (E* was about 10), and the color hardly changed even if the treated wood was exposed for a long time.