The article deals with book miniatures reflecting the history of the assassination of the first Russian saints-martyrs, from the two famous illuminated manuscripts – Radziwiłł Chronicle (Late 15 c.) and the so-called Silvestrovsky Sbornik (Sylvester Compilation, late 14 c.). Miniatures of one theme are shown against the background of the iconographic tradition that has developed over centuries of princes Boris and Gleb veneration. The nature of the selection of illustrative material, graphic topics, the ratio of drawings to texts allow us to conclude that there are genre requirements dictated by the type of works (chronicle story-hagiographic work). Ancient Russian artists were influenced by various texts telling about Boris and Gleb. The evidence of this is the contamination of motives and details that go back not only to the illustrated monument itself. Therefore, ancient book miniatures can not serve as an indisputable basis for determining the chronological sequence of the appearance of the main monuments of the Boris and Gleb cycle.