Abstract: Solution culture, subcellular fractionating procedure, electron microscopy examination and biochemical analysis were used to study the effects of calcium supply on subcellular distribution of cadmium, chloroplast ultrastructure and RuBPC and PEPC activity in maize seedlings under cadmium stress. Compared to no calcium supply under cadmium stress, calcium supply could significantly lower Cd content and increase Ca content in both organelles and cytoplastic fraction in roots and leaves of maize, while no such sighs were observed with cell wall fraction. In calcium supply treatment under cadmium stress, stroma lamellae in chloroplast of mestome sheath and grana and grana lamellae in mesophyll were better arranged, and much less osmiophilics appeared in chloroplast of mestome sheath, compared to that of no calcium supply treatment. It was also found that RuBPC and PEPC activity in leaves of maize under cadmium stress significantly increased by supplying Ca. It was concluded that calcium play a very important role in maintaning normal structure and function for plants under cadmium stress.