Information on a species' reproductive ecology can contribute to the pool of knowledge about avian natural history and life-history evolution. This is particularly true for species inhabiting remote and inaccessible regions. Here we report on the reproductive ecology of the Mountain Chiffchaff Phylloscopus sindianus, a warbler endemic to the Pamir Plateau (Central Asia), based on data from 22 nests observed on the eastern Pamir Plateau. The birds nested in thorny shrubs and their breeding season took place between mid-May and late June, during which a pair might make a single nesting attempt. Clutch size averaged 3.9 (3–5) eggs. Both parents undertook incubation and provisioned nestlings and the nestling period lasted 15.0 (13–18) days. The logistic growth rate constant of nestling body mass was 0.49. Nesting success, measured as the proportion of nests with at least one fledgling, was 68.2%, with predation explaining 57.1% of nest failures. Despite possible constraints on reproductive investment at high altitudes due to the harsh environment, comparisons of reproductive data from current and earlier studies of different warbler species show that higher-altitude birds do not produce different clutch sizes or eggs of different size compared to their congeners at lower altitudes.