Background and Objectives: With the spread of library software and the need to use it in libraries, the issue of evaluating their capabilities, the way users interact with them, and the factors influencing acceptance or non-acceptance, has become an important challenge and a fundamental aim, and researchers in the field of information technology and even librarians have become interested in this field of research. To investigate this interaction, researchers use different models that called technology acceptance models. Among the various models used in this field, the expectation-confirmation theory is the most important and practical one. Based on this, since the most important factor for determining the success or failure of a library software is the users, and since determining the level of user satisfaction in interacting with computer systems is one of the important aspects of determining the efficiency of those systems, the purpose of present study is determining the gap between the librarians' expectations of the capabilities of the system and their perceived usefulness, based on the expectation-confirmation theory.
 
Methodology: This research is applied in terms of purpose and in terms of implementation method, it is a survey with a descriptive-analytical approach. The statistical population of this research is all the librarians working in public libraries of Khorasan Razavi province who use the “Saman” system. The number of librarians who use the “Saman” system in Khorasan Razavi province is 220, and the sample size was determined using Cochran's formula. Therefore, the sample size of 141 people was selected and finally 130 questionnaires were completed and returned. The data collection tool in this research is a researcher-made questionnaire in which questions with a five-point Likert scale from “very little” to “very much” are included. This questionnaire was prepared by reviewing literature of the researches and from the items of questionnaires and checklists that previous researchers had used in the evaluation of library software and information systems. In this questionnaire, the investigated capabilities including information display, help, search and retrieval, general capabilities, and loan section were evaluated. For the validity of the research questionnaire, in all stages of the questionnaire preparation, the opinions of experts in the field of information science from different universities of the country who specialized in the field of library software were used. Cronbach's alpha coefficient was used to measure the reliability of the data collection tool.
 
Findings: The findings of the research showed that the average level of librarians' satisfaction with the functioning of the Saman system is higher than the average number of 3 (3.519); Therefore, librarians are highly satisfied with the performance of Saman system. Another finding of the research showed that the average expectations of librarians is equal to 3.935 and more than the average number of 3. Therefore, it can be said with 95% certainty that the expectations of librarians from the capabilities of the Saman system are also high. Also, the gap between librarians' expectations of the capabilities of the system and their perceived usefulness based on the expectation-confirmation theory is significant. Another finding of the research showed that there is a small gap between the average level of expectation and perceived level. The least gap was seen in the abilities of the loan section (-0.235) and the biggest gap was seen in the search and retrieval capabilities (-0.554). In general, the gap between the expectations of librarians from each of the features of the Saman system (information display, help, search and retrieval, general capabilities and loan section) and the perceived usefulness was also significant.
 
Discussion: The results of the research show the appropriate efficiency of different capabilities of the Saman system, but in order to improve the reduction of the gap between the expectations and the perceived usefulness of the users of the Saman system, it is suggested that the designers and the support group of the Saman system, for bring the level of satisfaction and the level of expectations as close as possible, among active librarians interested in cooperation, select people and investigate and inquire about expectations and other components that can help the evolution of the Saman system. It is suggested that the designers of the Saman system periodically check and evaluate the expectations of the users so that they can move in line with the expectations of the users and gain their satisfaction.