Fruiting and germination characteristics of the dominant plant species Rhododendron aganniphum var. schiaopeplum and their variation along the environmental gradients such as altitude (4183-4673 m), slope and aspect were studied at the alpine treeline ecotone on the southeastern Tibetan Plateau. The fruiting characteristics including fruit length, width, weight, seed number per capsule and 1000-seed weight of R. aganniphum var. schiaopeplum from different habitats were measured and compared, and the responses of seed germination to temperature and light were tested. The results showed that: (1) as cold-temperature stress increasing at higher altitude, the reproductive input of R. aganniphum var. schiaopeplum increased, with larger and heavier fruits, more seed number per capsule but smaller seeds than that from other environments; (2) slop aspect was the main factor affecting seed number per capsule with significantly larger seed number per fruit on the shady slope than that on the sunny slope, indicating a better reproductive ability on the shady slope; (3) seeds of the population in moderate soil moisture conditions (28.3%-32.5%) showed highest germination ability; (4) seeds of R. aganniphum var. schiaopeplum are photosensitive and cannot germinate in darkness; (5) in light conditions, germination percentage and rate are significantly affected by temperature, and the highest germination percentage and the most speedy germination showed at 25/5 ℃. This study investigated the relationship between fruiting and germination characteristics of R. aganniphum var. schiaopeplum and their habitat conditions, which provides basic data for the germplasm conservation and the dynamic prediction of the tree-line on the southeastern Tibetan Plateau in the context of climate change.