Background: Online information retrieval is a process the result of which is influenced by the changes in the emotional moods of the user. It seems reasonable to include emotional aspects in developing information retrieval systems in order to optimize the experience of the users. Therefore, this study aimed to identify the role of positive and negative affects in the information seeking process on the web among students of medical sciences. Methods: From the methodological perspective, the present study was an experimental and applied research. According to the nature of the experimental method, observation and questionnaire were used. The participants were the students of various fields of Medical Sciences. The research sample included 50 students of Shiraz University of Medical Sciences selected through purposeful sampling method; they regularly used World Wide Web and google engine for information retrieval in educational, Research, personal, or managerial activities. In order to collect the data, search tasks were characterized by the topic, sequence in a search process, difficulty level, and searcher’ s interest (simple) in a task. Face and content validity of the questionnaire were confirmed by the experts. Reliability of the questionnaire was tested by Alpha Cronbach. Cronbach’ s alpha coefficient (PA=0. 777, NA=0. 754) showed a high rate of reliability in a PANAS questionnaire. The collected data were analyzed using SPSS, version 20. 0; also, to test the research hypothesis, T-Test and pair Samples T-Test were used. The P<0. 05 was considered statistically significant. Results: The results showed that there was a significant association between the positive affect and users’ successful retrieval (P<0. 001). Also, there were significant associations between the negative and positive affect, type of search (P<0. 001) and quality of retrieved results of the web (P<0. 001) in the simple and difficult search. Finally, the impact of positive and negative affects before and after searching in the information retrieval result showed that there were significant associations between negative affects before the search and while doing the simple search (P<0. 001); also, a significant association was found between negative affects in the simple and difficult searches (P=0. 020). The results showed that the positive affects before and after the search had no significant effect during the search on simple and difficult search (P >0. 05). Conclusion: Information retrieval systems in the Web should identify positive and negative affects in the information seeking process in a set of perceiving signs in human interaction with the computer. The automatic identification of the users’ affect opens new dimensions into users moderators and information retrieval systems for successful retrieval from the Web.