Аннотация:The Large Aral Sea is a climate-forming reservoir of the Central Asia, which during the last 57 years has undergone significant metamorphism of the water area, the level of total mineralization of water in various parts of it, the coastline, the composition of bottom sediments and the bottom surface - and the biota inhabiting it. The investigations carried out on the material of the IORAN expeditions made it possible to trace the main changes in the bottom biota and ichthyofauna of the Large Aral Sea during the stage of ultragalinization of waters (the process of steady salting, which continues beyond the ultra-galaline physiological barrier of 75 ppt), during the stage of changes from 2002 to 2017. The last species of fish (Caspian aterin Atherina boyeri caspia and Black Sea plaice Platichthys flesus luscus), and mollusks (Syndosmya segmentum) inhabiting the Large Sea disappeared by 2004, with an increase in total mineralization in shallows above 90 ppt. Of the representatives of the bottom macrofauna, by 2015 only the larvae of the chaeronids Baeotendipes noctivaga have survived, from the pelagic-bottom by 2017, the crustacean Artemia parthenogenetica. The most diverse group of organisms inhabiting the ultra-galaline Aral during the studied stage were bottom microphytes (mainly diatoms and cyanoprokaryotes): in the newly formed biotopes stable associations of these creatures were formed, some of which were preserved in the Aral Sea, adapting to an extremely changing environment, others were planted, despite the growth of mineralization, and the third gradually died out. Against the background of the general growth trend of mineralization, it was possible to distinguish between the main formations of bottom microphyte cenoses.