Ranunculus kadzusensis is an endangered aquatic plant species that commonly reproduces in the rice paddies of Korea and Japan during winter and early spring. Here, we investigated the effects of main aquatic environmental factors-light, temperature, and water depth-on its growth, with the goal of seeking information that will contribute to its in situ conservation. As the amount of shading increased, biomass, maximum shoot length, number of branches, flowers, and fruits, main stem diameter, and maximum leaf length decreased. Although seed germination occurred under a 12-h photoperiod and at either 30/$20^{circ}C$ (day/night) or 20/$15^{circ}C$, most plants died at the higher temperature. Survival was 0% for surface-grown plant sets when tested in a wintertime pond experiment. The rate of maximum shoot extension was greatest for plants grown at depths of 50 and 100 cm versus those at 20 cm. Thus, we demonstrated that R. kadzusensis is intolerant of high temperatures and shade, which may explain why its growth is limited to paddies with no shading and where temperatures are low early in the year, before rice cultivation begins.