The function of CHST3 (carbohydrate sulfotransferase 3, Ensembl gene identifier ENSG00000122863) is as follows. Sulfotransferase that utilizes 3'-phospho-5'-adenylyl sulfate (PAPS) as sulfonate donor to catalyze the transfer of sulfate to position 6 of the N-acetylgalactosamine (GalNAc) residue of chondroitin (PubMed:15215498, PubMed:9714738, PubMed:9883891). Chondroitin sulfate constitutes the predominant proteoglycan present in cartilage and is distributed on the surfaces of many cells and extracellular matrices (PubMed:9714738). Catalyzes with a lower efficiency the sulfation of Gal residues of keratan sulfate, another glycosaminoglycan (PubMed:9714738). Can also catalyze the sulfation of the Gal residues in sialyl N-acetyllactosamine (sialyl LacNAc) oligosaccharides (By similarity). May play a role in the maintenance of naive T-lymphocytes in the spleen (By similarity). {ECO:0000250|UniProtKB:O88199, ECO:0000250|UniProtKB:Q92179, ECO:0000269|PubMed:15215498, ECO:0000269|PubMed:9714738, ECO:0000269|PubMed:9883891, ECO:0000303|PubMed:9714738}.