Abstract The modified polyurethane foam (PUF) with ammonium lignosulfonate was prepared by one-step water foaming method. The effects of ammonium lignosulfonate on its thermal stability and smoke suppression were investigated by thermogravimetric analysis, pyrolysis kinetics analysis, smoke density (Ds) and smoke toxicity analysis. The results showed that the addition of 15 % ammonium lignosulfonate (PUFA15) had the lowest mass loss of PUFs and the highest integral programmed decomposition temperature (870.8 °C). Its activation energy was the highest according to the Flynn-Wall-Ozawa method (110.1 kJ/mol), Kissinger method (181.1 kJ/mol), Starnk method (106.3 kJ/mol) and Coats-Redfern method (149.7 kJ/mol). In addition, PUFA15 had the lowest Ds (34.43) and the highest transmittance (66.74). This indicated that PUFA15 had good thermal stability and smoke suppression properties. The research results had a reference value for exploring the production of environmentally friendly PUF by biomass modification.