The relationship of urease act ivity with Hg and Cd was studied.Results showed a similar effect of Hg and Cd on urease regardless of its state whether solute, clay or soil.Hg+Cd's treatment was the highest in inhibition effect when Hg and Cd remarkably inhibited urease activity, meanwhile Hg was the strongest in ecot-oxicity.Urease activity could be used as an index of Hg or Hg+Cd pollution of the soil.Urease activity was influenced not only by Hg or Cd singly, but also by their interaction.The single-factor effect was still in dominance.Their effects on urease varied sharply because of the difference in its carrier, which plays an important role in protecting the enzyme and buffering the heavy metals.The solute-state urease did not have carriers and hence was more sensitive and susceptible to damage of heavy metals than the other two.Besides, temperature and concentration of urea enhanced the inhibition effect of Hg and Cd on urease activity.