Transboundary conservation is critical to halting global biodiversity loss, yet transboundary species represent a particular challenge in terms of who is primarily responsible for their conservation and how to coordinate between range states. Based on intensive field surveys from 2010 to 2023 and systematic data compilation from multilingual literature, we developed the first quantitative framework for assessing national conservation responsibilities for Siberian ibex (Capra sibirica) across its 11-country distribution. We integrated ensemble species distribution models with systematic conservation planning to identify 48 Landscape Conservation Units (LCUs), then applied an entropy weight method to quantify each country's conservation responsibility based on ecological importance, protection effectiveness, and national capacity. Our assessment reveals a three-tier classification: high-responsibility countries (China, Turkmenistan, Mongolia), medium-responsibility countries (Russia, Kazakhstan, Tajikistan, India), and low-responsibility countries (Kyrgyzstan, Pakistan, Afghanistan, Uzbekistan). China holds the highest responsibility (score = 0.678) due to its extensive LCUs (45.68 % of total LCUs) and high national capacity, though its low protected area coverage (15.18 %) indicates urgent need for conservation investment. While climate change threatens future habitat availability, anthropogenic pressures from infrastructure development and inadequate protection networks pose more immediate challenges. Our responsibility assessment framework provides a replicable protocol for other transboundary migratory species, helping countries work together more fairly and effectively to prevent extinctions.