Abstract: Commercial banks are an important industry for economic development in Thailand. Non-Performing Loans (NPLs), therefore, endanger the commercial banking system and affect overall economic scenery. This research studies the relation of macroeconomic and bank-specific determinants with NPLs base on quarterly data from 2005-2019 using autoregressive distributed lag (ARDL). The study revealed that there is a long-run equilibrium relationship of NPLs with Macroeconomic and bank-specific determinants. While the relationship between macroeconomic determinants and NPLs is significantly considered to be negative with gross domestic product (GDP) growth rate and exchange rate, the unemployment rate is considered to be significantly positive with NPLs. The direction of bank-specifics, i.e., return on assets, total loan and capital adequacy ratio are considered to be opposite NPLs and the lending interest rate affects NPLs positively and significantly. The results suggested that commercial banks along with the government and the policymakers should pay attention to guidelines for lending interest rates including the fluctuation of exchange rates, in order to restrict the NPLs and to ensure country’s financial stability in the long run.