North Eastern Eurasia is covered by permafrost which is the largest and the deepest in the world, and taiga forest (deciduous conifer larch) exists on it. It is expected that northern edge of taiga (taiga-tundra boundary) is greatly affected by global warming, and change in vegetation may cause greenhouse gas emission. Field observation on photosynthesis of larch and C and N isotope ratios of plants were carried out in taiga-tundra boundary ecosystem at Chokurdakh in 2008, 2009 and 2010 to investigate the response of the photosynthesis on various environmental factors. Observed rate of photosynthesis changed with PAR, and decreased when the chamber temperature was more than 22 ^oC. N content and N and C isotope ratios of larch needles varied among years and also among the sites. Needle δ¹³C was higher in 2009 than in 2008 and 2010, and needle N content was negatively consistent with δ¹³C. No significant differences of larch needle δ¹⁵N were found in 2009 and 2010. Larch trees are generally found on tree mound which consists of sphagnum, however, several trees were found growing at wet area where the landscape was similar to wetland. Larch needle δ¹³C at wet area was lower than the trees at the other sites, δ¹⁵N value and N content were also lower.