in a collaborative process, several independent organizations work together in order to achieve a specified goal and each of them is responsible for executing a part of the relevant process. Since the relevant process is executing through the flow of information and knowledge among the participating organizations, so facilitating inter-organizational knowledge transfer is suggested as a way to improve these process performance. Creating facilities is impossible without identification of existing barriers of inter-organizational knowledge transfer. The current paper tries to identify the barriers of knowledge transfer among public sector organizations using the study of existing literature and a case study of a collaborative process in tax determination process among tax administration, Bank and Municipality. The required information was gathered through semi-structured interview and coded and analyzed according to grounded theory. Findings show that “technical tools”, “governmental laws”, “organizational features” are the most influential factors of inter-organizational knowledge transfer.