The purpose of this paper is to investigate the level of awareness and use of open source integrated library system (ILS) by the library and information science (LIS) professionals in India. Further, it examines whether qualification, experience of using open source ILS and participation in open source community/mailing list by the LIS professionals affect their level of awareness and use of different open source ILSs. Design/methodology/approach: An online survey was conducted to assess the level of awareness and use of open source ILS by LIS professionals of India. In total, 408 responses were collected from LIS professionals in India, and the collected data were analysed using descriptive statistics and Pearson’s Chi-Square. Findings: The findings of the study reveal that the level of awareness and use of open source ILS, namely, Koha (Mean = 2.69, SD = 0.944) and NewGenLib (Mean = 2.19, SD = 0.703) are high among the LIS professionals in India. Koha is the most favoured open source ILS. The results reveal that educational background, experience of using open source software (OSS) and participation in open source community/mailing list affect their level of awareness and use of open source ILS. Practical implications: The paper will help decision makers to adopt and use popular open source ILS in their libraries. Originality/value: This paper is the first of its kind that explores the level of awareness and use of open source ILS by LIS professionals in India in a broad manner.