Fulvic acid (Henan ChangSheng Corporation) photoinduced degradation of non-UVA-absorbing herbicide amitrole (3-amino-1,2,4-triazole, AMT) as a way for its removal from polluted water was investigated in details. It was shown that the main primary species generated by fulvic acid under UVA radiation, triplet state and hydrated electron, are not directly involved in the herbicide degradation. AMT decays in reactions with secondary intermediates, reactive oxygen species, formed in reactions of the primary ones with dissolved oxygen. Singlet oxygen is responsible for 80% of herbicide oxidation, and •OH and O2−• radicals—for the remaining 20% of AMT. It was found that quantum yield of AMT photodegradation (ϕ365nm) decreases linearly from 2.2 × 10−3 to 1.2 × 10−3 with the increase of fulvic acid concentration from 1.1 to 30 mg L−1. On the contrary, the increase of AMT concentration from 0.8 to 25 mg L−1 leads to practically linear growth of ϕ365nm value from 1.8 × 10−4 to 4 × 10−3. Thus, the fulvic acid exhibits a good potential as UVA photooxidizer of organic pollutants sensitive to the singlet oxygen (ϕ532nm(1O2) = 0.025 at pH 6.5).