Arabidopsis thaliana plants showed an increased tolerance to high-intensity light when pre-exposed to medium-intensity light. This response, known as light acclimatization, depended on the quantity of light, the period of irradiation, and the quality of light. Among characterized acclimatization-induced cDNA clones, we identified a zinc finger protein rhl41 (responsive to high light) gene, that was rapidly up-regulated in proportion to the time of irradiation and the light intensity. Transgenic Arabidopsis plants over-expressing the rhl41 gene showed an increased tolerance to high-intensity light, and also morphological changes of thicker and dark green leaves. Interestingly, the palisade parenchyma was highly developed in the leaves of the transgenic plants, which is one of the long-term acclimatization responses in Arabidopsis plants. The anthocyanin content (a light protectant) as well as the chlorophyll content also increased. Antisense transgenic plants exhibited decreased tolerance to high irradiation. We propose that the RHL41 zinc finger protein has a key role in the acclimatization response to changes in light intensity.