The cocoa crop is an important source of income for many farmers in the region of Altamira-PA, and other neighboring regions. Cocoa production has great economic importance in this region and in much of the state of Pará. The objective of this study was to determine which species of weeds affect the culture of cocoa in Princesa do Xingu agricultural village, Altamira-PA. This survey followed a few steps: collecting, counting, drying and species identification. The phytosociological parameters frequency, density, abundance, relative frequency, relative density, relative abundance and the Importance Value Index (I.V.I.) were used to analyze the data. A total of 13 botanical families were identified, distributed in 27 species and 691 individuals. Families who registered highest number of individuals were: Cyperaceae (130), Poaceae (95), Fabaceae (89), Rubiaceae (89), Lamiaceae (66) and Verbenaceae (60), followed by Amaranthaceae (56), Plantaginaceae (48) and Asteraceae (44). The species Calopogonium mucunoides Std., Scoparia dulcis L., had occurred in 5 squares. Among the species, which showed the highest levels of importance value were: Alternanthera brasiliana (L.) Kuntze. (25.90%), Pycreus polystachyos (Rottb.) P. Beauv. (24.29%), Hyptis atrorubens Poit. (21.41%), Stachytarpheta cayennensis (Rich.) Vahl. (18.82%), Scoparia dulcis L. (18.62%) and Calopogonium mucunoides Std. (16.60%).