This work analyzes archaeobotanical microremains from burials of the fluvial shell mound Monte Castelo, located in the Guaporé Pantanal region, southwestern Amazonia. We investigated plant use through phytoliths and starch grains, extracted from ceramic pieces, soil sediments, and dental calculus of three burials from the Bacabal phase (4300 to 700 cal. BP). Monte Castelo was occupied between 6000 and 650 cal. BP (Furquim et al. 2021), and Bacabal is manifested in its upper layers as the last of the three recognized occupation periods, containing a large amount of botanical, faunal, and ceramic remains (Zimpel and Pugliese 2016). The general objective of the research is to provide an overview of the relationships established between these populations and the plants. As specific objectives, we seek to understand dietary habits and burial practices exercised. The methods for extracting the microremains are present in Coil et al. (2003), Pearsall (2015), and Wesolowski (2007, and the taxonomic identification used works such as Pagán-Jiménez (2015) and Piperno (2006). We interpret the results obtained in the context of cultural practices among indigenous peoples of the Amazon.