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nowadays, the significant increase in the banks' non- performing loans is one of the main disturbances for authorities because of its bad effects on the macroeconomic index in our country such as increasing credit risk, liquidity risk and finally bankruptcy risk. social gap in welfare programs, deviation in monetary policies, etc. are the other bad results of this phenomenon. meanwhile, due to our major effort to implement a riba-free banking system, the non-performing loans proportion to the overall banking demands may be taken by international supervisors as an index of iran's special condition.  studying the causes of npls is one of the research priorities to help decrease npls and to improve our monetary position. in this article, we survey those causes by using grounded theory. we have also benefitted from the opinions of some banking officials to gather data and analyze them. finally, we show that npls causes can relate to both macroeconomic and microeconomic factors. we can also relate microeconomic factors to self-banking factors and borrowers' behavioral factors.