Hydroxylamine (NH₂OH) is one of the most active trace forms of nitrogen in oceans, and it is the key intermediate product of many nitrogen cycle processes, such as ammonia oxidation, dissimilatory nitrate reduction to ammonium and anaerobic ammonia oxidation. Therefore, it is an important component of the marine nitrogen cycle network framework. Concurrently, NH₂OH is an important precursor of the greenhouse gas nitrous oxide (N₂O), closely related to the production and release of marine N₂O. Accordingly, a systematic understanding of the source and sink, spatiotemporal variations, and regulatory mechanisms of NH₂OH in the ocean is essential to understand the oceanic nitrogen cycle and climate effects. However, the nanomolar concentration of NH₂OH in the ocean and its complex and active migration and transformation processes render the oceanographic community’s understanding of NH₂OH unclear. Current research on marine NH₂OH is systematically reviewed, focusing on the potential source and sink processes of NH₂OH, the determination methods of NH₂OH, the possible contribution of NH₂OH to marine N₂O, and the distribution characteristics and potential impact factors of NH₂OH in the ocean. Finally, the problems and difficulties in determining NH₂OH and the possible mechanisms affecting its distribution are summarized, and suggestions and prospects for future research on marine NH₂OH are discussed.