Indonesia has many large and small islands so that it has diversity related to cultural activities, especially water areas. One of the water activities in Indonesia is trade in the Musi River, Palembang. The purpose of this study was to determine the mathematical concepts contained in mobile trading activities on the Musi River. The research subject is a traveling merchant who trades Palembang local food using traditional boats on the Musi River. The research used is qualitative with an ethnographic approach. Data collection techniques in this study are literature study, observation, interviews and documentation. The conclusion of this study is that mobile trading on the Musi River indirectly applies several mathematical concepts, such as build space (ball), flat (rectangular), comparison, and social arithmetic.