Formaldehyde can pose a huge threat to human health due to its’ carcinogenic effect. Carbon materials asadsorbents are widely applied to remove formaldehyde hazards. However, most carbon materials with disadvantages of thelimited number of surface functional groups and the lack of suitable pore structure suffer from low adsorption rate for theadsorptive removal of formaldehyde. To improve the adsorption capability, oxygen (O) and nitrogen (N) elements co-dopedporous viscose-based activated carbon fiber (N-O-ACF) was prepared via oxidation-hydrothermal treatment. First of all, theO atom can be introduced into ACF through chemical oxidation. Then, with the help of the O atom bridging effect, N atomscan be efficiently incorporated into ACF, and the content of the N element is as high as 7.13 wt.%. Thus, an improvedadsorption performance of N-O-ACF for formaldehyde removal was achieved with the support of the synergistic effect of Nand O elements. The adsorption capacity of N-O-ACF for removing formaldehyde increased up to 226 mg g-1, while only161.5 mg g-1 was obtained for original ACF. The excellent formaldehyde adsorption capacity indicates that N-O-ACF may bea promising adsorbent in the field of indoor air purification.