The data about pathways of biosynthesis, regulation of metabolism, physiological and ecological functions of organic acids production by fungi of various ecological groups are generalized and analyzed. Metabolism and excretion of organic acids by fungi depend on many factors, including nutrient and mineral conditions, temperature, and various stresses. An increase in the excretion of organic acids, especially oxalic acid by fungi is often a response to stress. Organic acids production by fungi has important ecological and physiological significance because it is related to changing the surrounding microconditions and inf luencing the biotic and abiotic interactions of microorganisms in community. Organic acids are involved in the formation of mycorrhiza, the processes of plant pathogenesis, and are also one of the key factors in wood decay. The ability to acidification largely determines the geochemical role of fungi and their importance in the weathering of rocks and the processes of primary soil formation.