Data on ningyoite [CaU(PO₄)₂ · 2H₂O] occurrences in uranium ores and on deposits with ores composed entirely or largely of this mineral are considered. Most of the recent findings of ningyoite mineralization are confined to infiltration deposits, and only sporadic ones, to pegmatites and hydrothermal deposits. The geological settings and mineral assemblages indicate that ningyoite ores are formed from neutral or slightly alkaline solutions at higher Eh values relative to other types of uranium blacks (uraninite, coffinite) and are localized in the reducing zone at the boundary of redox zoning. The factors that testify to the decisive role of microbiological processes in the formation of monomineral ningyoite ore are considered. All hydrogenic deposits (occurrences) of ningyoite ore known to date in Japan, Bulgaria, Canada, Kazakhstan, and Siberia belong to the same ground-infiltration genetic type.