Abstract: Based on Pinus thunbergii growing in Dalian City, we developed the time series of tree radial growth, tree-ring stable carbon isotope ratio (δ¹³C) and intrinsic water use efficiency (WUE_i) in the period of 1951-2010, and studied their variation and the climate related significance. Radial growth of the pines showed a decrease trend, tree-ring δ¹³C decreased slightly, but WUE_i increased significantly (P<0.05) after 1980. Climate factors affected tree-ring width, δ¹³C and WUE_i of the pines, and the effects showed seasonal variation. Temperatures respectively showed positive and negative correlations with radial growth of the pines in summer and winter, while monthly precipitation and relative humidity in June had positive correlations with tree-ring width in general. Monthly temperature had weakly positive correlations with δ¹³C and WUE_i in March-September, and slightly negative correlation during the rest months of a year. Precipitation and relative humidity respectively had negative correlations with δ¹³C and WUE_i in general. The rapid warming environment in the city contributed to the WUE_i increase of urban trees.