The author discusses the findings of the comprehensive study of the role and potential of the national union catalogs (NUC) in the context of developing Open Science ecosystem of the Commonwealth of Independent States (CIS). Based on the comparative analysis of legal, organizational and technological models of the Republic of Armenia, Republic of Belarus, Republic of Kazakhstan, and the Russian Federation, the author demonstrates that these systems are not only the corporate cataloguing instruments but also critically important infrastructural platform for further aggregation and distribution of open science resources metadata. The general trends are revealed, i. e. national library centralizing role, MARC-compatible formats, increasing networking, and national context (platform choice, collection specific features). The author argues that further NUC advancement toward integration with institutional repositories and open access global services will make the strategic vector for strengthening cooperation and science and increasing visibility of research outcomes in the CIS countries.