Abstract: A pot experiment was carried out to investigate sulphur supply and mycorrhizal inoculation on the growth and quality of onion (Allium cepa L). Onion seedlings were grown in the Perlite pots and irrigated with Long Ashton nutrient solution. The plants were inoculated with arbuscular mycorrhizal fungi Glomus versiforme, and there are three levels of sulphur supplies, 0.1, 1.75 and 4 mmol/L. The results show the biomass of onion is significantly increased under the mycorrhizal inoculation due to the higher phosphorus nutrient status under different sulfur supply levels, while the biomass is not significantly affected for the sulphur treatments without the inoculation, and the contents of total sulphur and organic sulphur of the shoot are increased with the increase of S supply. The effect of the mycorrhizal inoculation on sulphur nutrient status varies with the sulphur supplied levels, and the contents of total sulphur and enzyme produced pyruvic acid (EPY) in onion plants under the inoculation are significantly higher than those without the inoculation when 1.75 and 4 mmol/L sulphur are supplied, while the content of total sulphur is decreased when 0.1mmol/L sulphur is supplied. The arbuscular mycorrhizal inoculation appears to make a substantial contribution to the sulfur status of onion plants, and may thus have a strong effect on quality of host plants.