We present a genome assembly from an individual male Bombus sylvestris (the Forest Cuckoo Bee; Arthropoda; Insecta; Hymenoptera; Apidae). The genome sequence is 303 megabases in span. Most of the assembly is scaffolded into 24 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 23.6 kilobases in length. Gene annotation of this assembly on Ensembl has identified 13,025 protein coding genes.