Capuchin monkeys (Sapajus libidinosus) in several populations use stone tools to crack open encapsulated fruits. One of the resources they process with those tools are cashew nuts. During the maturation changes, the cashew nuts turns easier to crack, because when dry (late season) the husk became more fragile. We know that some wild chimpanzees (Pan troglodytes) adjust their selection of tools according to the properties of the processed nut, using harder (stone) tools when the nuts are harder, and softer (wood) tools when the the nuts are dry and easier to crack. We think this same process could happen to the capuchin monkeys at Serra da Capivara National Park. We tested if the cashew nut properties (fresh x dry) change the selection of tools by those monkeys. The capuchins use stone tools to open both fresh and dry nuts as part of their natural foraging behavior. Our results show that capuchins used significantly larger tools to process fresh nuts, and males selected larger stone tools than females. The number of hits used to open a nut was influenced only by the hammer size (fewer hits with larger hammers), for fresh and dry nuts. We found that these capuchins adjust the selection of stone tools to different maturation stages of cashew nuts. This research complied with the International Primatological Society (IPS) Guidelines for the Use of Nonhuman Primates in Research and had the approval of the Brazilian environmental agency (IBAMA – 37615-2). Grant: ERC, FAPESP.