Rapid increases in betel-nut plantations in the 1980s and 1990s have significantly affected the environment and biological conditions of slopeland in Taiwan. Impacts of converting from forested land to betel-nut plantations on the environment are serious enough to have attracted much concern from government and environmental groups. A series of research on this topic has already been carried out. However, most of these researches were focused on problems of soil and water conservation associated with slopeland betel-nut plantations. In order to examine differences in microclimatic conditions between betel-nut plantations and natural hardwood forests, the average air temperature, relative humidity, earth temperature, solar radiation, and rainfall above and below the canopies of these 2 stands were continuously monitored. The available continuous records from January 2000 to January 2001 indicate that there are no differences between these 2 study areas in temperatures above and below the canopy. However, the yearly average earth temperature (at 5-cm depth) of the betel-nut plantation was 2.3℃ higher than that of natural hardwood forest, which was significant at the 1• level. The multilayered and denser canopy of natural hardwood forest stands consumes much solar energy by evapotranspiration and photosynthesis than does that of betel-nut stands. Therefore less energy is available for heating the soil which results in lower earth temperatures than found in betel-nut plantations. However, the difference is less significant during rainy days and at night. Relative humidity is strongly influenced by canopy cover. The transportation of moisture can be hindered under a heavy forest canopy which results in higher relative humidity. Statistical results indicate that relative humidity was significantly under-canopy conditions of natural hardwood stands, whereas above the canopy, it was not as high. In addition, the long-term weather records at Lienhuachih meteorological station of Taiwan Forest Research Institute also reveal that the annual average air temperature, especially for summer seasons, shows a tendency of increase after 1980. Further studies are needed to clarify the effects of the rapid increase in betel-nut cultivation on climate changes in the Lienhuachih area.