Purpose: The present research aims to investigate librarian's job characteristics based on their demographic analysis in Tehran academic libraries under the authority of Ministry of Health and Medical Education.Methodology: It has been carried out with survey method and two questionnaires (job characteristics and demographic characteristics) were used to collect the data. The research population includes 133 librarians of Tehran University of Medical Sciences, Shahid Beheshti University of Medical Sciences, and University of Social Welfare and Rehabilitation Sciences. Totally, 118 questionnaires were completed and returned.Findings: The findings indicate that job characteristics between librarians are evaluated on average level, and among demographic characteristics, there is only significant correlation between workplace and job identity, and other demographic variables are not significant predictors to librarians' job characteristics.Conclusion: Increased job autonomy between librarians gives them a sense of achievement, boosts their performance and productivity, and motivates them to try more for doing their best job. Also, with appropriate and professional application of librarians in different workplaces, their job identity will increase and their job gets meaningful and with intrinsic motivation they do the activities which gives high meaning to them and their workplace.