AbstractThe hydroxyl (OH) radical, which is generated in polluted dew water on leaf surfaces of the Japanese apricot (Prunus mume), is known to be a potent oxidant. In order to investigate the effects of the OH radical formed in polluted dew water on the photosynthesis and growth of 3‐year‐old seedlings of P. mume, OH radical‐generating solutions simulating polluted dew water were sprayed in the early morning as a mist throughout a growing season onto the leaf surfaces of seedlings growing in experimental greenhouses. Four OH radical‐generating solutions (0, 6, 18 and 54 μM H2O2 with Fe(III) and an oxalate ion) were used in the mist treatment. Five months after the beginning of treatment, the leaves exposed to the mist containing 54 μM H2O2 showed a significantly smaller maximum CO2 assimilation rate (Amax) and stomatal conductance (gs) as compared to the leaves exposed to the mist containing 0 μM H2O2. Exposure of P. mume seedlings to the OH radical‐generating mist had caused a reduction in the dry weight and relative growth rate (RGR) of the above‐ground parts (stem + branch) at the end of the growing season. A significant positive correlation was shown between RGR and Amax. Thus, the effects of oxidants generated in polluted dew water on leaf surfaces can be considered to be a cause of the decrease in leaf photosynthesis and growth of P. mume.