Thermostable alpha-glucan phosphorylase-catalyzed enzymatic copolymerization of alpha-D-glucose 1-phosphate (Glc-1-P) with its analogue monomer, alpha-D-glucosamine 1-phosphate (GlcN-1-P), from a maltotriose primer was performed to produce non-natural heteroaminopolysaccharides composed of Glc/GlcN units, that is, alpha(1 -> 4)-linked glucosaminoglucans. The GlcN units in the products were further converted to N-acetyl-D-glucosamine (GlcNAc) units by N-acetylation. The structures of the products were evaluated by the MALDI-TOF MS, H-1 NMR, H-1-H-1 and COSY NMR measurements, which were completely different from those of the natural glycosaminoglycans. The degrees of polymerization and Glc/GlcN compositional ratios of the products were relatively dependent on the Glc-1-P/Glc-1-P/Glc(3) feed ratios. The noncrystalline natures of the present materials were supported by the X-ray diffraction measurement.