We studied the relationships between earlywood/latewood width, stable carbon isotope ratio (δ13C) of cellulose, and soil moisture at a dry and a wet site in Yakutsk, eastern Siberia, which differed considerably in soil water conditions. Recharge of soil water by snowmelt in spring and subsequent drought in summer provided a marked seasonal contrast in soil water conditions between the earlywood and latewood formation period. Ring index was calculated by dividing each earlywood/latewood width by the 5-year averaged width for each individual. In order to determine whether drought influenced the ring index-δ13C relation, the ring index time series were compared with δ13C time series. We collected wood samples from eight Larix gmelinii (Rupr.) Rupr. and four Pinus sylvestris L. trees from the two sites and measured the earlywood and latewood widths and δ13C of earlywood and latewood formed during the years 1996–2000. At the dry site, seasonal soil water content variation corresponded to seasonal δ13C variation of tree rings. We found negative ring index-δ13C correlations in latewood for both species at the dry site mainly dominated by Pinus but not in latewood of Larix at the wet site dominated by Larix. Decrease and/or early cessation of latewood growth and increase in δ13C under drought conditions possibly explain this negative correlation. This suggests the growth limitation of trees in this region by drought and the prospects of reconstructing past drought with latewood δ13C of the dry site.