An attempt to study the ancient spores and pollen grains of the intramontane peat bog at Doi Inthanon, Chiang Mai Province, was carried out in order to reconstruct the pollen and spore diagram of past deposition in the above mentioned area. The sphagnum peat core (1A) of 2-metre depth, obtained from Associate Professor Kosum Pyramarn and Assistant Professor Dr.Thanawat Jarupongsakul, wrapped in plastic sheeth and stored in the refrigerator, was treated. In each 2-centrimetre peat core, a one-centrimetre cube was used for grain sampling. These subsamplings were treated by Jarupongsakul's method (1987) to extract the spores and pollen grains. Then, the grains obtained were mounted on the microscopic slides by using silicone oil, AK 2000, as mounting media. In order to reconstruction the plant community, the identification and analytical investigation of the deposited grains were done through a light microscope and a scanning electron microscope. Interpretation of pollen and spore diagrams from peat bog (1A) at an estimated 2,565 metres above sea level indicated that from about 4,300 years ago up to present, the upper montane rain forest was dominant in this area. The reconstruction also helps confirm that the recently collected pollen grains and spores from the plants in the sampling site are of the same vegetation type. Moreover, this evidence also indicated that the climate in this vicinity could be divided into six zones according to the change of cool and warm weather by using the fluctuation of temperate plants as an indicator. This evidence further supported the theory that the Holocene climate was unstable. The occurrence of Polygonum and grass pollen grains in all zones might also indicate that this area was deforested by human cativities.