Measurements of photosynthetic activity of Polygonum weyrichii var. alpinum were carried out in a field at the timberline of Mt. Fuji and in the laboratory in summers of 1982 and 1983. In order to measure photosynthesis at remote alpine locations, measurement systems were divided into several units small enough for carrying by one person. In addition, special care was taken in collecting and transporting plant materials for photosynthetic measurement in the laboratory. Good agreement was found for the light-photosynthesis curves between the field and laboratory measurements.