The characteristics of the mucous cells located in gills of the fish Cyprinus carpio were investigated. Mucous cells were determined from gill arc, gill body, primary and secondary lamellae. Mostly mucous cells had oval-globular shape throughout all regions. Histochemical analysis of the gill of Cyprinus carpio showed that mucous content included glycogene and/or oxidizable dioles (PAS +), neutral or acid-rich (PAS/AB pH 2.5 +), sialic acid residues (KOH/PAS +) and strong acid sulphated (AF +) glycoproteins (GPs). Except these mucosubstances, carboxyl groups and/or with sulphate esters (AB pH 2.5 +) strong sulphate (AB pH 0.5 +) (AF/AB pH 2.5 +), O-sulphate esters (AB pH 1+) glycoproteins were also determined.