Gangliosides, sialic acid-containing glycosphingolipids, are responsible for neurogenesis and synaptogenesis which are essential for vertebrate nervous system. N-Acetylgalactosaminyltransferase (Galgt) is glycosyltransferase that plays essential role during complex gangliosides biosynthesis. Expression of Galgt increases at the late stage of development which can be evidence for complex gangliosides role in nervous system development and differentiation.Sialidases are responsible enzymes for sialic acid removal from glycoproteins, glycolipids or oligosaccharides. Neu1 is one of the mammalian sialidase which catabolizes sialoglycoconjugates in lysosomes. Neu1 gene mutations in human result in lysosomal storage disease called sialidosis. Created Neu1 knockout mice model have demonstrated similar symptoms with sialidosis type II. In sialidosis patients, increased ganglioside levels are detected in visceral organs but not in brain. In vitro studies have demonstrated that GM3 is a substrate of Neu1. Until this research, role of Neu1 enzyme on glycosphingolipid metabolism in the absence of complex gangliosides has not been investigated. Therefore this study have been provided comparision of 2-and 4-month-old Neu1-/-, Galgt-/- and Neu1-/-Galgt-/- mice to WT mice and each other by molecular biological, biochemical, histological, immunohistochemical and behavioral analysis in cortex, cerebellum and thalamus regions. In the concept of this thesis, we found effect of single and double deficienct of Neu1 and Galgt enzymes on the distinct cellular events (apoptosis, ER stress, oxidative stress), altered glycolipid and oligosaccharide metabolism, nerve cell death,oligodendrocyte intensity decrease, impairment in locomotor activity, motor coordination, memory capability as age dependent and region specific manner.