Resumo. Studies on xyloglucan (XG) extracted from Hymenaea courbaril L. (jatoba) seeds showed that this biopolymer has biological activity that enhanced wheat coleoptiles growth. In apple tree micropropagation, the culture medium containing XG combined with agar induced a higher multiplication rate, rooting rate and root length than medium solidified with agar only. The purpose of this study was to determine the effect of XG from jatobá seeds extracted from jatoba seeds collected in Sinope/MT (XGS) and Cuiabá/MT (XGC), and from XGC hydrolysed with a cellulase (XGCH), as well from Tamarindus indica seeds (XGT) collected in Bahia/BA, on the growth of in vitro cultured Arabidopsis thaliana plantlets. In the first experiment, XGCH (0.25, 25 and 250 nM) or XGC (0.5, 50 and 500 nM) were added to a liquid half-strength MS medium. In the second experiment, XGs from several origins were compared: XGC (500 nM), XGS (1200 nM) and XGT (800 nM), using culture medium solidified with 6 g.L-1agar. Arabidopsis thaliana L. seeds germinated in Petri plates for 4 to 5 days were transferred to culture media containing the different concentrations of XGs and cultured in a growing room. When the plantlets were cultured in a liquid medium, their growth was very slow in the presence of XGC and XGCH at the highest concentration tested, and it was faster at the lowest concentration. In the semi-solid culture medium, XGs also reduced growth. It was concluded that XGs can play a biological role in Arabidopsis thaliana (L.) Heynh. plantlets, stimulating or inhibiting the root system growth and the lateral root formation. These opposite effects varied according to the plant specie that furnished the seeds containing XG, as well as the place where the seeds were collected, to the XG form used (hydrolyzed or not) and to its concentration in the culture media.