One of the most effective ways to study the library activity success is to work with unsatisfied readers’ requests to receive information corresponding to the library profile. The article contains material obtained in the course of research activities within the framework of the scientific project, which assumes, in particular, the study of the level of users’ satisfaction with the quality of collections. Therefore, the purpose of the article is to present the results of the analysis of the current situation with unsatisfied requests in the departments of the State Scientific Technological Library of SB RAS, its impact on the quality of the library collections and reader service, on decisionmaking to improve working activities. In the course of work, the authors used scientific methods of analysis and generalization both of theoretical elaborations and library statistical data. The analysis of refusals over the past five years has allowed us to formulate a number of problems leading to the emergence of unsatisfied readers’ requests. The revealed considerable changes both in the organizational and functional structures of the library and the technology of servicing readers have led to decentralization of the process of work with unsatisfied requests thus negatively influencing its coordination and effectiveness. The basic stated reasons are deterioration of information resources and imperfection of reference apparatus. Special consideration deserves the situation within the categories of priority for the scientific library: proceeding from the received data, refusals to them made 34 % from the total amount of unsatisfied requests. The authors suppose that the conclusions drawn on the results of the study, though being the upper “cut off” the problem of unsatisfied requests, are an objectively necessary basis for optimizing the processes of stack formation and servicing readers of SPSTL SB RAS.