The article explores the spreading of Enlightenment ideas within the Basilian monasteries of the L'viv eparchy in the second half of the 18th century. Based on inventory descriptions from the L'viv archives, the repertoire of Enlightenment books was revealed, which usually circulated in the largest monastic libraries of the L'viv eparchy. Research is undertaken within the religious history context, especially within the Catholic Enlightenment in Europe, that rationalized and deepened reforms of Trident. To protect the fundamental Christian dogmas, Catholicism reinterpreted them in a "new" language, more understandable for its time. Without any doubt, studying the library collections is appropriate for the mentioned research because books are the sources of particular ideas and beliefs. Research has found that Enlightenment books were rare in the Basilian monastery libraries of the L'viv eparchy until the 1770s. The article examines only the two largest monastery libraries of the Basilians in the L'viv eparchy -in Pidhirtsi and L'viv St. Onuphry. A collection of French books (the language of Enlightenment and international communication) was found in the Pidhirtsi monastery in the late 1760s -early 1770s. For example, samples of "Les Aventures de Télémaque" (1699) written by archbishop François Fénelon or "L'École du monde, ou Instruction d'un père à un fils" by French playwright and "journalist" Eustache le Noble. L'viv St. Onuphry monastery library in 1778 had a few Enlightenment books as well. Since Basilians studied philosophy, there was a great collection of philosophical books. For instance, there were samples of treatises written by such well-known philosophers as Christian Wolff, Friedrich Christian Baumeister, Ignatz von Metzburg. To sum up, it can be argued that Enlightenment books were not popular in the mentioned monastery libraries. During the research, no texts of Voltaire, Diderot, or Montesquieu were found. However, the obtained results reaffirmed that it is necessary to explore the issue of the Enlightenment ideas in the Basilian monasteries of early modern Ukraine in more depth.