The isotopic fractionation could contribute to understanding the Cd accumulation mechanisms in plant species. However, there are few of systematical investigations with regards to the Cd isotope fractionation in hyperaccumulator plants. The Cd tolerant Ricinus communis and hyperaccumulator Solanum nigrum were cultivated in nutrient solutions with varying Cd and EDTA concentrations. Cd isotope ratios were determined in the solution, root, stem and leaf. The two investigated plants were systematically enriched in light isotopes relative to their solutions (Delta Cd-114/110(plant-solution)= -0.64 parts per thousand to -0.29 parts per thousand for R. communis and -0.84 parts per thousand to -031 parts per thousand for S. nigrum). Cd isotopes were markedly fractionated among the plant tissues. For both plant species, an enrichment in light Cd isotopes from solution to root was noted, followed by a slight depletion in light Cd isotopes from root to shoot. Noticeably, the chelation process has caused lighter Cd isotope enrichment in the root of R. communis and S. nigrum. Further, the good fits between Delta Cd-114/110(root-plant) and In F-root (or between Delta Cd-114/110(shoot-plant) and In F-shoot) indicate that Cd isotopic signatures can be used to study Cd transportation during the metabolic process of plants. This study suggests that knowledge of the Cd isotope ratios could also provide new tool for identifying the Cd-avoiding crop cultivars.