The male mucus gland is present in all species of bees, exception for meliponines. In bees, the function of the mucus glands is not certain so far and its contribution to form the female espermatecal fluid is not assured. With the aim to contribute to the knowledge of the mucus gland in bees we carried out a histochemical study of the gland in mature, adult males of Bombus morio, focusing on the histochemical nature of the secretion. The males were collected around the forest fragments into UFSCar, Campus Sorocaba. The glands were fixed and analysed under routine microscopy and for histochemistry techniques: Periodic Acid Schiff (PAS), Bromophenol Blue (BB), Sudan Black (SB) and Critical Electrolyte Concentration (CEC) variant. The results showed that the mucus gland is constituted by a pair of large, thick tubular structures, which presented their distal portion more dilated and corn shaped. The glandular cells are columnar and in the apical portion present several apocrine vesicles being released into the gland lumen. The histochemistry showed that gland secretion is very complex and contains protein (BB), neutral polysaccharide (PAS), as well as lipid (SB). The luminal gland secretion presents a background of homogenous content, presenting little dark dots stained by all techniques used for this work. The investigation of the nucleolar activity (CEC) showed that the mucus gland epithelium is evolved in protein synthesis, presenting nucleoli developed and much RNA in the cytoplasm.