Introduction: The present research attempts to study the theoretical foundations of thesaurus construction before and after internet and identify the problems of thesaurus construction in Iran from the point of view of thesaurus makers and translators of the published thesauri..

Methods: The research population was 6 thesaurus makers (AbdolHossein Azaragn, Abbas Hori, Fatemeh Rahadoost, Fariborz Khosravi, Molookolsadat Beheshti, Mohammad Hadi Yaeghoub Negad), who have published 12 thesauri since 2003. This was a qualitative study done for the first time in the academic environment of LIS. Data collection was done through interview. After interviewing the research population and studying the related literature, the data was classified into different groups and then analyzed according to the measures discussed in methodology section.

Findings: The findings indicated that: 1) The theoretical foundations of thesaurus construction have changed after the introduction of web and the revolutionalized environment of information technology, 2) Most problems experienced by the interviewers were of managerial and administrative nature and almost all of the thesaurus makers suffered from lack of adequate and proper interaction among responsible institutions, at institutional and national levels. The other problems could be enumerated as: weakness of storage and retrieval systems, the undocumented queries in reference departments of libraries and information centers, weakness of information literacy of subject specialists, shortage of budget and lack of appropriate evaluation measures and thesauri criticism in the LIS environment.

Conclusion: Many of problems that thesaurus makers experienced were of managerial and administrative nature and almost the entire thesaurus makers suffered from lack of adequate and proper interaction among responsible institutions, at institutional and national levels.