We present a genome assembly from a male specimen of Satyrium pruni (Black Hairstreak; Arthropoda; Insecta; Lepidoptera; Lycaenidae). The assembly contains two haplotypes with total lengths of 869.86 megabases and 870.75 megabases. Most of haplotype 1 (99.02%) is scaffolded into 23 chromosomal pseudomolecules, including the Z sex chromosome. Haplotype 2 was assembled to scaffold level. The mitochondrial genome has also been assembled, with a length of 15.46 kilobases.