The growth response of Mongolian pine (Pinus sylvestris var. mongolica) to climate was studied at three sites in the Hulun Buir steppe on the eastern Mongolian Plateau, China. Correlation analysis revealed two patterns of response: (1) trees on two sites in the upstream section of the Yimin River are strongly limited by temperature and precipitation during the growing season from April to September, and (2) trees in the convergence area of the downstream section of the Yimin River and of the midstream section of the Hailar River are sensitive to precipitation during winter (December–January) and early spring (April) as well as to the early growing season temperature (April and June). These responses can be attributed to the positions where groundwater, recharged by the runoff from summer to autumn (July–September), could supply sufficient water needed for tree growth. Therefore, the patterns of growth–climate responses and of climate variation trends in this steppe region should be considered for the management and afforestation of Mongolian pines.