This study reports a novel ultraviolet (UV) absorber, N-dihydroxy ethylene cyanoguanidine (NDEC), which was synthesized from dicyandiamide and glyoxal. The NDEC compound was characterized by Fourier-transform infrared spectrum and nuclear magnetic resonance. NDEC was grafted onto cotton fabric through covalent bonding by the pad–dry cure method. The optimal finishing conditions were that the mass concentration of NDEC was 5 g/L, baking time 240 s and temperature 140℃. The UPF value of cotton fabric treated under optimal finishing conditions reached 50+ and was minimally reduced (to 47) after 50 laundry cycles. The breaking strength and thermostability of the original cotton fabric were preserved after treatment. Successful grafting of – C≡N and –C=N groups onto the treated fabric was confirmed in the Fourier-transform infrared spectrum. Meanwhile, the finished cotton fiber remained smooth, as confirmed by scanning electronic microscopy.