This paper describes the secondary uranium minerals of the Perus district in Sao Paulo State, Brazil. The minera's may be genetically related to the igneous intrusions of the area. The uranium minerals are found in fractures and cracks of pegmatites and tourmaline bearing granites, which have been derived from a granitic magma, responsible also for the formation of the Pirituba granite. However, metamorphic rocks such as micaschists, amphibolites and hornfelses may be also found in the area. Several research methods have been utilized for the study of the uranium minerals, not only for identifying the various mineral species, but also for finding new physical and chemical data for the minerals themselves. The following methods have been used: optical microscopy and X-ray crystallography as the main techniques, and UV fluorescence, radioctivity detection, infra-red spectroscopy, thermal behaviour and chemical procedures as additional methods. Twelve different species of uranium minerals have been described in this paper: autunite, meta-autunite I, meta-autwrte II, hydrogen autunite, phosphuranylite, mineral "X", torbenite, meta-torbenite I, meta-torbenite II, uranophane, beta-uranophane, and uranium opal. A few of those minerals, meta-autunite II and meta-torbenite II, are artificial species, obtained by meating of autunite and torbernite respectively. Unfortunately, not all the mentioned minerals have been studied thoroughly bythe use of all described methods of research, due to occurrence of small amounts. Such are the cases with phos phuranylite, mineral X and hydrogen-autunite. The mineral "X", thus provisionally designated, is probably a new mineral species. Its physical properties were thoroughly investigated. However, the small quantity available has not allowed trustoworthy chemical analysis. Nevertheless, the physical properties and some spectrographical analysis indicate the mineral as an uranyl phosphate, isostructural with phosphurany ite. Besides the description of the uranium, the primary minerals of pegmatites and tourmaline granites have been investigated, for field evidences have indicated these rocks as the probable source for uranuim. Albite, microcline, tourmalines, lepidolite, quartz and apatite were throughly investigated as far as their physical and chemical properties are concerned. Apatite seems to be the primary source of uranium. This type of genesis has been reported in several other areas of the globe, where U+4 ions replaces Ca+² in the apatite crystal structure. The very sensitive method of radioactivation analysis has revealed a rate of 56 ppm U for apatite of Perus, which represents a high percentage, when one compares this figure with the amount of U, found in the other pegmatite minerals (3 ppm). The underground water carrying CO2 and O2 in solution, have attacked, oxidized, and dissolved the apatite, forming acid mineralizing solutions containing UO2+², Ca+², HC0(3)-1 and PO4-3 ions. Through a neutralizing action, in contact with alkaline solutions, such mineralizing liquids have precipitated autunite and torbernite. Phosphuranylite has been formed by autunite alteration through pH modification, and the mineral "X" originated by precipitation of Mg-bearing solutions. Uranophane and beta-uranophane resulted from the interaction of coroidall silica and mineralizing fluids, whose ions have provoked collold fluculation. This mechanism explains the colloform and radiated habit of such minerals. The uranium-bearing opal had probably a similar origin, that is, by f oculation of colloidal silica solutions in contact with electrolites.