Abstract: Plant-soil carbon stable isotope characteristics of riparian herbaceous ecosystem were ana-lyzed by measuring the δ¹³C value of plant tissues from four typical riparian herbaceous plants, which were Cynodon dactylon, Trifolium repens, Festuca arundinacea and Imperata cylindrical, and that of soil organic carbon (SOC) from different vertical depths along Dongfeng Port River in Qingpu District, Shanghai. The result showed that T. repens and F. arundinacea were C3 plants while C. dactylon and I. cylindrical were C4 plants. There was no significant difference between the δ¹³C va-lue of stem and leaf, litter and root of the four herbaceous plants. The surface SOC δ¹³C value of C3 and C4 plants strips showed different trends with soil depth, which could be related to the background SOC δ¹³C value, soil carbon stable isotope fractionation effect and plant root distribution depth as well. Plant input was the main source of SOC and the δ¹³C composition of plant organisms had direct effect on the SOC δ¹³C value. The δ¹³C value of plant components were significantly correlated with the δ¹³C value of SOC. The SOC content and δ¹³C value were significantly correlated in the four herbaceous plants strips. The SOC content and δ¹³C value showed linear negative correlation in C3 plant strips and linear positive correlation in C4 plant strips.