Hydrolyzes aryl-N-acetyl-beta-D-glucosaminide (aryl-beta-GlcNAc), aryl-beta-GalNAc and chitin oligosaccharides. Can hydrolyze rapidly the artificial substrates p-nitrophenyl-N-acetyl-beta-D-glucosaminide (PNP-beta-GlcNAc) and 4-methylumbelliferyl-beta-GlcNAc, and is slightly active on p-nitrophenyl-beta-GalNAc. This enzyme is not processive, i.e. when it hydrolyzes (GlcNAc)n, both products, (Glc-NAc)n-1 and the terminal GlcNAc, are released before the enzyme attacks a second molecule of (GlcNAc)n or (GlcNAc)n-1. Hydrolysis of terminal non-reducing N-acetyl-D-hexosamine residues in N-acetyl-beta-D-hexosaminides. Inhibited by mercuric ions, PNP-beta-Glc, PNP-beta-Gal, PNP-alpha-GlcNAc, and PNP-beta-S-GlcNAc. Optimum pH is 7.0 with (Glc-NAc)n (n=3-6) as substrate and 5.8 with (GlcNAc)2 as substrate. Optimum temperature is 35-40 degrees Celsius. Glycan degradation; chitin degradation. Homodimer. By (GlcNAc)2. Belongs to the glycosyl hydrolase 20 family.