Abstract: Quercus aquifolioides as a dominant broad-leaved tree species in southeastern Tibet, plays a crucial role in soil and water conservation, as well as water source retention in high-altitude regions. Currently, seed insect infestation is a major constraint affecting natural regeneration in secondary forests, seedling cultivation, and industrial utilization. This study investigated the seed insect infestation status of Quercus aquifolioides and its impact on seed quality across different altitudes (3000–3500 m) on Sejila Mountain. The aim was to clarify the extent and characteristics of pest damage to provide a foundation for the conservation and utilization research of Quercus aquifolioides resources.The experimental results demonstrated that: 1. Infestation rate decreased significantly with increasing altitude. ** At any given sampling time, the infestation rate was highest at 3000 m (reaching 95.05% in mid-August) and lowest at 3500 m (80.08% in mid-August). Concurrently, infestation rates increased with later collection dates. At the same altitude, infestation rates rose progressively from mid-August to mid-September (increasing from 95.05% to 98.90%). 2. Seed quality exhibited a U-shaped pattern across the altitude gradient**, being poorest at 3200 m and optimal at 3500 m. 3. Thousand-seed weight and seed volume fluctuated with both collection time and altitude.In mid-August, thousand-seed weight increased with altitude (850.78 g at 3000 m vs. 1152.08 g at 3500 m). However, by mid-September, thousand-seed weight at the mid-altitude (3200 m) decreased drastically (640.63 g). Similarly, seed volume peaked at 3400 m in mid-August (2.628 cm³), while volumes at mid-to-high altitudes (3200–3300 m) were significantly reduced by mid-September.4.Seedling emergence rate increased with altitude, being highest at 3500 m (reaching 35% in mid-August). Emergence rates were significantly lower at low (3000–3100 m) and mid (3200 m) altitudes. Seeds collected in mid-September generally exhibited reduced emergence rates.