Abstract: During the period of August-November, 1960, observations were made to investigate the characteristics of radiation balance, heat balance, and microclimate in the forest of Hainan, Kwangtung. The results of the observations may be summarized as follows: 1) In the forest the radiation intensity and the heat exchange are much weaker than on the open ground. 2) The radiation heat is mainly spent on the soil heating and evaporation in the forest, but mainly on the air heating and evaporation on the open ground. 3) In the forest the soil and air temperatures are lower, but the humidity is higher than on the open ground. Therefore, the microclimate in the forest is cool and moist, while that on the open ground is hot and dry.