The thesis investigates external debt sustainability in Armenia, Kazakhstan, Kyrgyz Republic and Moldova on the basis of variables associated with the foreign economic activity of these countries. After discussing the current problems and vulnerabilities of countries related to the current account deficit and debt structure, sustainability zones are estimated in based on GDS. Based on that, as of 2017, all 4 countries met sustainability criteria. However, the results of the ADF test demonstrated the opposite, having established that all countries except Moldova did not achieve debt sustainability. The outcomes of accounting method did not show sufficient evidences of sustainability of current account balances in 4 countries.The thesis investigates external debt sustainability in Armenia, Kazakhstan, Kyrgyz Republic and Moldova on the basis of variables associated with the foreign economic activity of these countries. After discussing the current problems and vulnerabilities of countries related to the current account deficit and debt structure, sustainability zones are estimated in based on GDS. Based on that, as of 2017, all 4 countries met sustainability criteria. However, the results of the ADF test demonstrated the opposite, having established that all countries except Moldova did not achieve debt sustainability. The outcomes of accounting method did not show sufficient evidences of sustainability of current account balances in 4 countries.