Azolla is a floating water fern that live in symbiosis with blue-green algae Anabaena, it has the ability to fix atmospheric nitrogen. Azolla plants stimulated many studies in all over the world. Redox processes occurring in water ecosystems at sediment-water, rootplant-sediment, rootplant-water are the base of all the interface transformations. The aim of this investigation was to describe redox changes during the growing of water fern. During 14 days of experiment at laboratory conditions, dynamics of Eh in nutritive solution and soil sediment were pointed out. An 1 cm -depth gradient in redox potential was stated in the range of 100-130 mV for the nutritive solution, and 200-300 mV for the pond sediment. An active role in aerating the nutritive solution by Azolla caroliniana Willd. was stated.