The purpose of the present study was to analyze the interdisciplinary relations of “Library Science and Information Science”. For this purpose the subject categories of citing and cited journals of these fields were investigated in JCR database during the period of 1987-1997 and 2003-2013, and through the comparsion of obtained results the impact of information technology on the development of “LIS” interdisciplinarity was investigated. Methedology of the research was co-citation analysis of journals in scientometrics studies. Also the research was performed using the conventional techniques of scientometrics including Bradford law, Ward hierarchical clustering approach in statistical software SPSS, and the new measure including Proximity index. Research community includes citing and cited journals of 56 “LIS” journals during 1987-1997 and 83 journals during 2003-2013 in Journals Ctiation Report (JCR) database. The results showed that “LIS” has been influenced by other subject categories more than affecting them. For example, the number of journals which “LIS” cited from 1758 (in the first period) has increased to 5303 (in the second period). Co-occurrence matrix of core citing and cited subject categories was analyzed, and three main clusters in the first period and seven clusters in the second period were drawn. In general, the amount and quality of co-occurrence of subject categories in clusters showed that the domain and variety of affecting and affected subject categories were expanded in the second period. Structural similarity of clusters for affecting and affected subject categories calculated. Results showed that structural similarity of clusters in the second period was %10 higher than in the first period. Also, the Structural similarity of affecting clusters of “LIS” was more than affected clusters. Assessment of difference between subject categories groups by ANOVA and Tukey Post hoc tests showed that there were differences between all numbers of citing and cited groups.