Fibrosis is the end-stage change of damaged tissues in various human diseases, which can lead to permanent scarring or organ malfunction. Hypoxia leads to oxidative stress, mitochondrial dysfunction, and inflammation in dysfunctional organs and tissues. Oxidative stress resulting from the overproduction of reactive oxygen species plays a central role in the fibrosis of injured organs. This review addresses the updated knowledge of the relationship between hypoxia and tissue fibrosis mediated by the reactive oxygen species pathway. Moreover, novel anti-fibrotic strategies are discussed, which may suppress reactive oxygen species and organ fibrosis.