Major collections include the following: stock of the old Han schools (schools of the feudal domains) and the Tokugawa Shogunate Succession Documents that were inherited from the former Imperial Library; the Ito Bunko (Ito collection) and the Shirai Bunko (Shirai collection), consisting of old books on herbalism; the Modern Political and Constitutional History, comprising materials on the modern political history, which were collected as a high priority considering the nature of a post-war national library as a facility for the Diet; the collection of official gazettes and statutes of Japan and foreign countries; the Ashihara Eiryo Collection, a collection of materials related to ballet and chanson inherited from the Ueno Branch Library; and the Nunokawa Bunko (Nunokawa collection) (the collection formerly possessed by Kakuzaemon NUNOKAWA), which concentrated on materials related to the history of publications and culture.
代表的なコレクションとして、帝国図書館から引き継いだ旧藩校蔵書、江戸幕府引継書類、本草学関連の古書からなる伊藤文庫・白井文庫や、戦後の国会図書館が議会のための図書館であるという性格から重点的に受け入れた近代政治史関連史資料からなる憲政資料、国内外の議会・法令関係資料、支部上野図書館で旧蔵していたバレエ・シャンソン関連資料の蘆原英了コレクション、出版文化史資料を中心とする布川文庫（布川角左衛門旧蔵書）などがある。