Influence of La3+ on the accumulation of trace elements (75Se, 56 Co, 83 Rb, 48 V, 95 mTc, and 67Ga) in chloroplasts of cucumber seedling leaves was studied by a radioactive multi-tracer technique. At the same time, chloroplast contents of different concentrations of La3+ treatment were calculated. It was observed that chloroplast contents peaked at 0.02 mM La3+ treatment and that the uptake and distribution of these trace elements in chloroplasts of cucumber seedling leaves are different under different La3+ treatments. With the increase of lanthanum concentrations from 0.002 to 2 mM, the uptake percentages of 75Se, 56 Co, and 83 Rb presented an obvious increase and then sharply decreased in contrast to the non-lanthanum treatment, whereas there appeared a sharp decrease and then restored control level in the uptake of 48 V. The other two trace elements, namely 95 mTc and 67Ga, were accumulated only in the presence of 0.02 mM La3+. The results indicate that lanthanum treatments to growing the cucumber lead to the change of trace element uptake in the chloroplasts of leaves, which suggest that lanthanum might influence the accumulation of trace elements in chloroplasts of cucumber seedling leaves by regulation of various ion transport mechanisms, thus affecting the photosystem of leaves.