Bioavailability of soil heavy metals refers to the degree of absorption and accumulation of soil heavy metals by organisms and toxicity to organisms.Kunshan City,typical of the Yangtze River Delta,was chosen as case for study on bioavailability of soil heavy metals.A total of 126 soil samples were collected and analyzed.Results show that available Cd ranked first in concentration,and its bioavailability reached up to 63.75%.Significant differences were observed in bioavailability of heavy metals between different function zones,Cd,Cu,Ni,Pb and Co were the highest in the smelting and plating industry zone,Cr in the chemical industry zone and Zn in the vegetable production zone.Differences in bioavailability of Cd,Cr,Cu,Pb and Zn were also found between soil types,which were in a decreasing order of Wushan soil > Qingni Soil > Huangni Soil,as well as between soils of different parent materials which were lined in an order of fluvial and marine sediment > lacustrine sediment.It was also found that the effect of soil forming parent materials was greater than that of soil type on the bioavailability,and that the bioavailability and contents of available heavy metals declined with the depth in soil profile.Marked positive correlation existed between concentrations of heavy metals in rapeseed and concentrations of bioavailable heavy metals in the soil.Zn and Cd showed the highest enrichment coefficient,posing the highest potential risk.Analysis of total concentrations & bioavailability of soil heavy metals and their total concentration in plant revealed that Cd was the dominant pollutant that threatens safety of agricultural production and groundwater.