Abstract: A measurement was made on the vertical direction tree ring stable carbon isotope ratio (δ¹³C) and tree ring width of Pinus sylvestris var. mongolica in northern Daxing’an Mountains of Northeast China, with the relationship between the vertical direction variations of the tree ring δ¹³C and tree ring width analyzed. In the whole ring of xylem, earlywood (EW) and bark endodermis, the δ¹³C all exhibited an increasing trend from the top to the base at first, with the maximum at the bottom of tree crown, and then, decreased rapidly to the minimum downward. The EW and latewood (LW) had an increasing ratio of average tree ring width from the base to the top. The average annual sequence of the δ¹³C in vertical direction had an obvious reverse  correspondence  with the average annual sequence of tree ring width, and had a trend comparatively in line with the average annual sequence of the tree ring width ratio of EW to LW above tree crown. The variance analysis showed that there existed significant differences in the sequences of tree ring δ¹³C and ring width in vertical direction, and the magnitude of vertical  δ¹³C variability was basically the same as that of the interannual δ¹³C variability. The yeartoyear variation trend of the vertical  δ¹³C sequence was approximately identical. For each sample, the δ¹³C sequence at the same heights was negatively correlated with the ring width sequence, but the statistical significance differed with tree height.