The thermal decomposition kinetics of 5-fluorouracil was studied by thermogravimetric analysis methodology. The decomposition activation energy was calculated by using Ozawa method by means of TGA in nitrogen atmosphere. Moreover, the decomposition mechanism and pre-factor were obtained by Coats-Redfern and Achar methods, respectively. It is found that the decomposition activation energy of fluorouracil is 105 kJ·mol.1. The decomposition mechanisms obtained by Coats-Redfern and Achar methods are G(α)=[-ln(1-α)]2/3 and f(α)=1.5(1-α)[-ln(1-α)1/3 respectively, lnA is 21.40 min-1.