Recent research at the National Museum in Warsaw led to a discovery of a previously unnoticed collection of music sources. Alongside liturgical manuscripts from 13-17th centuries, described elsewhere, the Museum houses a collection of early music prints, which is not extensive (13 volumes with 20 titles), but for a number of reasons deserves a closer inspection; among the prints items regarded as lost during the Second World War, as well as rare or unique copies are found. The prints include seven volumes of polyphonic music from the turn of the 16th and 17th centuries, three liturgical books, two cantionals and the score of J. B. Lully's 'Proserpine'. The author analyzes their contents, traces origin and evaluates their importance for researchers.