Zhang, H., Zhu, L., Zhang, C., Ning, Y. and Zhang, Y. 2015. Effect of water stress on dry mass accumulation and allocation in sweet potato based on stable isotope analysis. Can. J. Plant Sci. 95: 263-271. Pot experiments were conducted to study the effect of water stress on the dry mass accumulation, allocation, ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) activity and stable carbon isotope composition in sweet potato (Ipomoea batatas L.). Three water regimes (50, 75 and 100% field water capacity, respectively) were investigated. Water stress effects on dry mass accumulation, allocation, gas exchange, stable carbon isotope composition and Rubisco enzyme activity were detected in sweet potato at different stages (seedling, vegetative, early maturity, and late maturity). In addition, relationships between Rubisco activity and photosynthetic rate, dry stress allocation and Δ¹³C under different water regimes were explored. The allocation of dry mass and Δ¹³C in leaves, petioles, stems and roots exhibited highest level in soil with 100% moisture content at different growth stages. The photosynthetic rate, transpiration, stomatal conductance, and RuBisCo activity of sweet potato at different growth stages also increased with increasing soil water content. The regression equations between the activity of RuBisCo and photosynthetic rate in 50, 75 and 100% field capacity were y=0.675x - 1.846, y=0.798x - 1.370, and y=0.516x 3.887. A positive correlation between dry mass allocation and Δ¹³C was observed. Water stress could affect dry mass accumulation, allocation, gas exchange, RuBisCo activity, and Δ¹³C content in sweet potato organs during plant development stages.