Abstract: Rhododendron thymifolium is a dominant species in alpine azalea shrub land in Eastern Qilian Mountains. The horizontal and vertical distribution of root biomass for R. thymifolium and of other associated plant species were measured under the shrub canopy and in the gaps between plants of R. thymifolium, and seasonal trends were monitored. Coarse and fine-root biomass, and other species root biomass decreased with increasing soil depth. For R. thymifolium, 90% of fine root biomass was located in the 0-20 cm soil layer, and root biomass under the shrub canopy was greater than that in the between-plant gaps. The fine-root biomass of R. thymifolium was less during the germination period and pre-dormancy periods; the fine roots grew rapidly from June, and reached peak values in July. Peak values always occurred earlier in the surface layer than in the deep layer, and roots in gap areas appeared earlier than those in the shrub canopy area. Gaps between shrubs were regions of active fine root growth. Root biomass of other species began to decline from the sprout period, and was low in July, then reached a maximum at the end of the growing season. The annual average dead root biomass was greater than live root biomass, the dead∶live root biomass ratio increased with soil depth.