Cucujus cinnaberinus and Boros schneideri are saproxylic insects, an important group of organisms linked with deadwood. Both are rare protected species, relicts of primeval forest. Observations of both species in the Knyszyńska Forest in 2018 and 2019 showed that they occur in forests protected under different conservation regimes and in sustainably managed forest. Specimens of C. cinnaberinus were present on many snags of various tree species in nature reserves and also in sustainably managed forest, where the insects were found on single dead trees, within retention patches, and in representative sample areas (RSAs). Specimens of B. schneideri observed in sustainably managed forest were found in reference forests, retention patches and also on single Scots pine snags. These observations from the Knyszyńska Forest suggest that it is possible to balance economic imperatives with the need to protect rare species in sustainably managed forest.