The history of vegetation has been registered in the sediments of lake Mimi since about 11 000 BP, The initial vegetation traced is a tundra which, under severe climatic conditions, lasted for about 1000 years. The herb tundra was progressively replaced by shrub tundra: a willow phase (Salix). followed by a dwarf birch phase (Betula cf. glandulosa) have been traced. These were followed by an afforestation phase characterized by an aspen community (Populus tremuloides) al about 10 000 BP. Spruce succeeded the aspen community, probably as an open black spruce (Picea mariana) community with some dwarf birch and green alder (Alnus crispa). An outstanding Alnus cf. crispa pollen peak (48%), supported by the annual pollen influx values, at the end of the spruce phase, could be interpreted as a return of colder climate that favored the expansion of this shrub over forest. This event would date about 9750 BP. An open fir (Abies balsamea) forest followed, and changed to the balsam fir – white birch (Betula papyrifera) forest (climax domain), which prevailed until now. The richer sites supported sugar maple (Acer saccharum) – yellow birch (Betula alleghaniensis) community and fir – yellow birch stands since 6200 BP. Six radiocarbon dates and annual pollen influx values are offered, and some ecological problems related to the interpretation of the pollen diagram are discussed.