Abstract. The objective of this study was to investigate the effects of water stress in sweet potato (Ipomoea batatas L. [Lam] ‘Georgia Jet’) on biomass production and plant-water relationships in an enriched CO2 atmosphere. Plants were grown in pots containing sandy loam soil (Typic Paleudult) at two concentrations of elevated CO2 and two water regimes in open-top field chambers. During the first 12 d of water stress, leaf xylem potentials were higher in plants grown in a CO2 concentration of 438 and 666 μmol mol−1 than in plants grown at 364 μmol mol−1. The 364 μmol mol−1 CO2 grown plants had to be rewatered 2 d earlier than the high CO2-grown plants in response to water stress. For plants grown under water stress, the yield of storage roots and root: shoot ratio were greater at high CO2 than at 364 μmol mol−1; the increase, however, was not linear with increasing CO2 concentrations. In well-watered plants, biomass production and storage root yield increased at elevated CO2, and these were greater as compared to water-stressed plants grown at the same CO2 concentration.