Biographical information is available through the National Library of Romania. The library has about 7000 biographical works, as welll as other biographical materials such as letters in its collection. The catalog is searchable on the library's website. The library itself is located in Bucuresti:
Biblioteca Nationala a Romaniei
Bulevardul Unirii 22
030833 Bucuresti 3, Romania
In addition, there are city libraries throughout Romania. Each has a collection of biographical books. You may want to check the library nearest where your ancestor is from or the county (judet) capital where he or she is from. For example, the Library of Metropolitan Bucuresti has some 2000 biographical works.
Both of the sites listed are in Romanian. Information about these libraries in Engliah can also be obtained from the European Library.