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Cadmium (Cd) is an industrial and environmental pollutant. It has toxic effects on root tip growth and morphogenesis of onion (Allium cepa L.). Onion roots were germinated in 0, 2, 5, 10, 25, 50, 100, 200 g/ml doses of CdSO4 salt. Then root tips were fixed, dehydrated and paraffin embedded. Afterwards, material was sectioned on a microtom (7 m thickness) and stained by Acridine orange fluorescent dye and cytochemical methods for DNA and RNA staining. Results show that Cd induces morphological changes such as cell vacuolization, nucleus and cytoplasm condensation and nucleus margination. It also causes decreases nucleoplasmic ratio and cell death induction. It was also observed that Cd toxicity has a threshold level (10-25?g/ml concentrations). In doses higher than this threshold, cells are irreversibly committed to death. Therefore in concentrations lower than 25 g/ml , the mode of cell death is apoptotic-like cytological features and necrosis happens in higher concentrations.