Collateral is a significant challenge for small and medium enterprises (SMEs) in acquiring formal credit. Bank market concentration can cause to increase collateral demand through enhancing bank market power. This study explores the relationship between bank market concentration and the collateral challenges faced by SMEs in accessing bank credit by employing a probit regression model. The analysis utilizes a sample of over 25,000 firms from 19 developing Asian nations. The datasets combine firm-level data sourced from the Business Environment and Enterprise Performance Survey (BEEPS) with country-level financial data obtained from the Global Financial Development Data (GFDD) which are provided by the World Bank. The results reveal a significant positive correlation between bank market concentration and the collateral challenges encountered by SMEs in developing Asian countries. In markets characterized by high levels of banking concentration, financial institutions tend to exhibit risk-averse behavior, manifesting in an increased propensity to demand collateral for both SME and large enterprise loans. Consequently, this heightened bank concentration exerts additional pressure on SMEs in acquiring bank credit. To foster an environment conducive to SME financing, countries with high levels of banking concentration should enact regulatory measures aimed at managing and constraining market concentration levels.