The cupuassu’s seeds are similar to cocoa, being possible to apply fermentative techniques used to obtain nibs and cupulate. The aim of this work to study the physicochemical transformations during the cupuassu´s seeds fermentation. For this purpose, frozen seeds from a pulp processing industry were fermented in three batches of 20 kg for seven days at room temperature. During the fermentation process, seed mass temperature, dimensions, density and composition of the kernels, color indexes (L*, C* and H*), microbiological analyzis (mesophiles, molds and yeasts), cut-proof, physicochemical analyzis (pH, acidity and glucose reducing sugars and non sucrose reduction) and centesimal composition (ashes, lipids, proteins and carbohydrates) were analyzed from triplicates. The results were expressed as dry basis. During the fermentations, the great temperatures were reached. The maximus were 43,44 and 47 ºC in three fermentations. It was observed during the fermentation process: seed darkening (L*) and color intensity reduction (Chroma), pH increase, sugar reduction and acidity reduction. The ash, lipid and protein contents were not significantly influenced by the fermentation time. According to the cut test, the kernels of 3rd fermentation, whose maximum temperature was higher, were classified as type 2 and the others as type 3. The values of apparent density, dimensions, mass and composition of seeds demonstrated that during the fermentation there was a decrease in volume with a higher proportion of cotyledon compared to testa. There was an increase in counts of total mesophiles aerobic microorganisms, molds and yeasts, during the fermentative process.