This article studies the factors influencing user satisfaction with online services of information units in the central libraries of Tarbiat Modarres University and University of Tehran. A total of 300 questionnaires were distributed among MSc and PhD students of the two universities. About 40 percent of respondents were from Engineering Faculty and about 30 percent were studying in Humanities Faculty. The respondents included 76.7 Master students and 20.3 percent PhD students. The majority of respondents were male (86.5%), and only 10.5 percent were female. The results revealed that six factors including network data transfer speed, information up datedness, number of retrieved documents, familiarity with search strategy, number of searching databases, and relevancy of retrieved documents had positive impact on user satisfaction. But no connection was found between user satisfaction and librarian's assistance in searching. In the end, a few suggestions are made for improvement of services.