In the present paper we describe for the first time the ultrastructure of the male reproductive system of aphids using Phyllaphis fagi as a representative. Paired testes of this species consist of three follicles each, arranged in a rosette, the walls of the proximal part of vasa deferentia cling together, accessory glands are club-shaped and elongated whereas the ejaculatory duct is reduced. Our study also shows that vasa deferentia, accessory glands and ejaculatory duct are histologically very simple. All of them are composed of cubical epithelium of secretory type. The epithelial cells are rich in rough endoplasmic reticulum, Golgi complexes and produce small heterogeneous vacuoles. The apical membrane of these cells forms microvilli. The reproductive system epithelia stand on thin basal lamina. Outside the basal lamina thin muscle fibres are observed. Histochemical staining shows that secretion filling the lumen of vasa deferentia and accessory glands contains proteins and polysaccharides.