We have previously shown that chondroitin 6-sulfotransferase (C6ST) catalyzes transfer of sulfate not only to position 6 of GalNAc residue of chondroitin but also to position 6 of Gal residue of keratan sulfate. In this study, we examined the sulfation of sialyl lactosamine oligosaccharides by C6ST. C6ST catalyzed transfer of sulfate to NeuAc alpha 2-3Gal beta 1-4GlcNAc (SLN), NeuAc alpha 2-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4GlcNAc (SL1L1), NeuAc alpha 2-3Gal beta 1-4(6-sulfo)GlcNAc beta 1-3(6-sulfo)Gal beta 1-4(6-sulfo)GlcNAc (SL2L4), and their desialylated derivatives, but not to NeuAc alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc (SLe(x)). The sulfated product formed from SLN was degraded with neuraminidase and reduced with NaBH4. The resulting sulfated disaccharide alditol showed the same retention time in SAX-HPLC as that of [3H]Gal(6SO4) beta 1-4GlcNAc-ol. The sulfated product formed from SLN was also degraded by a reaction sequence of neuraminidase digestion, hydrazinolysis, deamination, and NaBH4 reduction. The final product was coeluted with [3H]Gal(6SO4) beta 1-4anhydromannitol in SAX-HPLC. These observations show that C6ST could transfer sulfate to position 6 of Gal residue of SLN. Incorporation of sulfate into SL2L4 was much higher than the incorporation into SL1L1, suggesting that sulfate moiety attached to adjacent GlcNAc residue may stimulate the transfer of sulfate to Gal residue. The recombinant C6ST also catalyzed sulfation of the sialyl lactosamine oligosaccharides, indicating that a single protein catalyzes sulfation of chondroitin, keratan sulfate, and sialyl lactosamine oligosaccharides. These results raised a possibility that C6ST may be one of the candidates involved in the biosynthesis of sulfated sialyl Lewis x ligand for L-selectin.