The photodegradation process of ofloxacin in ultrapure water at different pH (3,7 and 11) and dissolved oxygen concentration (DO=9 and 0 mg/L) was investigated under UVA-LED irradiation. The results showed that the photodegradation follows first-order-kinetics, mainly direct photolysis. When dissolved oxygen exists, the self-sensitized photolysis could significantly promote the photodegradation. Under different DO conditions, the photodegradation efficiency and rate were the fastest at pH=7, followed by pH=11 and the slowest at pH=3. The main reason for the difference is that the photonic yield of ofloxacin varies with pH value. The analysis of degradation products and their formation process showed that the degradation pathways of ofloxacin was mainly demethylation, piperazinyl ring cleavage/oxidation, hydroxylation and decarboxylation. The degradation pathways and products of ofloxacin under different pH and DO conditions were slightly different, but have a significant influence on the process of products generation and further degradation over time. The above research results clarified the effects of pH and DO on the photodegradation of ofloxacin.