Though it has been reported that the accumulation of Cd in plant tissue increases with the decrease of the pH in soil, the mechanism of Cd accumulation in plant has not yet been clarified. Therefore, we investigated the effect of rhizosphere pH condition on the Cd accumulation in a soybean plant root, which is a gate for Cd uptake, using 109Cd tracer and an imaging plate (IP). Cadmium uptake by root tissue was found to be a fast reaction, since the amount of Cd uptake reached the plateau within about 2 hours (its time constant was about 20 minutes), Cd was easily transported into root apoplast, and moreover, its dynamics did not depend on an environmental pH condition (pH 4.5, 6.5). However, it was suggested that the amount of Cd taken up from the root was much higher in acidic conditions. Through image analysis taken by the IP, the accumulation and translocation of Cd were studied in roots.