The temperature measurement at southwest-facing edge of a rubber forest was conducted in a calm tropical region of Xishuangbanna, Yunnan, China in January 1998, and the daytime thermal characteristics and their time-space variations nearby the edge of the rubber forest were discussed. There was an obviously thermal effect at forest edge. The depth of edge influence on soil surface temperature was up to 13 m from the edge into the forest. Soil surface temperature reached its highest at 4.5 m outside the forest. The highest air temperature occurred at 0 m of the edge. The heat transfer nearby the edge was quite different in number and in direction. Outside the forest, the heat was transferred from ground to air on almost daytime, while at interior of forest, was opposite after the noon. The heat was transferred from the rubber canopy to the ground. At the forest edge, such variation was complex, depended mainly on location and time.