In a search for new and effective analgesic substances from the Brazilian biodiversity, the present study evaluates the chemical composition and antinociceptive potential of the methanol extract and a pure compound obtained from the seeds of Garcinia achachairu Rusby (Clusiaceae). The methanolic seed extract was directly subjected to purification by column chromatography and the purification was monitored by thin-layer chromatography. The main isolated compound was identified as Guttiferone A by comparison of conventional spectroscopic data (IR, NMR-1H and $^{13}C$) to the literature data which was isolated for the first time from this plant. When evaluated in the acetic acid-induced nociception model in mice, the methanolic seed extract had an $ID_{50}$ (Inhibitory dose) of 13.1 (11.23-14.91) mg/kg and a maximal inhibition of $72{pm}4%$. In the same model, Guttiferone A had an $ID_{50}$ of 4.54 (3.29-6.24) mg/kg and a maximal inhibition of $73{pm}5%$. The methanolic seed extract and Guttiferone A were also active in pain models induced by formalin, capsaicin, glutamate and carrageenan. These data suggest that the antinociceptive effect of Guttiferone A partly depends on its interference with the synthesis or activity of the cytokine TNF-${alpha}$, the keratinocyte-derived chemokine KC, and/or $PGE_2$. These data support, at least in part, the use of G. achachairu in folk medicine and suggest that this plant is an important source of compounds with a suitable profile for development as new and effective medicinal agents to treat pain processes.