Cadmium is a widespread, non-essential heavy metal, which is toxic to plant organisms. Zinc is an essential element, involved in important metabolic processes, such as activity and synthesis of proteins and nucleic acids, photosynthesis, and is required for normal plant growth. The aim of this study was to determine the effect of cadmium (10 μM) and zinc (50 and 100 μM), and their combinations, on duckweed (Lemna minor L.). Growth, content of hydrogen peroxide, malondialdehyde, carbonyls, activity of lipoxygenase and presence of heat shock proteins were observed as indicators of oxidative stress. It was found that cadmium (10 μM) inhibited growth and caused oxidative stress, which was evident by the increased contents of hydrogen peroxide, malondialdehyde and carbonyls, and increased activity of the lipoxygenase. Higher concentration of zinc (100 μM) caused a moderate oxidative stress, during which the reduced growth and increased content of hydrogen peroxide and carbonyls were present. Zinc at a concentration of 50 μM did’t cause oxidative stress. In combined action of cadmium (10 μM) and higher concentration of zinc (100 μM) it was observed that zinc alleviated effects of cadmium. The growth rate was higher, lipid peroxidation and activity of lipoxygenase were reduced, and an additional isoform of heat shock protein, molecular weight ~69 kDa, was present. In combination of cadmium and zinc, when zinc was present in lower concentration (50 μM), the results did’t show reduction in oxidative stress.