The bulk of rat brain neutral β- N-acetylhexosaminidases (2-acetamido-2-deoxy-β- d-hexoside acetamidodeoxyhexohydrolase, EC 3.2.1.52) were present in the cytosol fraction. They were not bound by concanavalin A-Sepharose while the acid β- N-acetylhexosaminidases were all bound. The neutral β- N-acetylglucosaminidase had a pH optimum of 5.2 and K m of 0.57 mM, while the neutral β- N-acetylgalactosaminidase had the highest reaction rate at pH 6.0 with a K m of 0.12 mM. No divalent ions activated either of the enzymes. The glucosaminidase lost more than 90% of the activity in 30 min at 50°C. The galactosaminidase was heat-stable and lost only 10–20% of its activity after 3 h at 50°C. The neutral glucosaminidase was inhibited by free N-acetylglucosamine but not by N-acetylgalactosamine. The reverse was found for the neutral β-galactosaminidase. Two enzymes were separated almost completely by hydroxyapatite chromatography. Heat stability of the separated activity peaks suggested that the neutral β- N-acetylgalactosaminidase, which was not bound to hydroxyapatite, may be specific to the galactosaminide substrate. The neutral β- N-acetylglucosaminidase may, on the other hand, have some activity toward the galactosaminide substrate. Both of the neutral enzyme activities were highest during the first postnatal week in rat brain in contrast to the acidic enzyme which showed peak activities during the second and third weeks. These results confirmed and expanded earlier observations by Frohwein and Gatt in calf brain. The relationship of these enzymes to the hexosaminidase C in human tissues is less certain at the present time.