TO optimize the sensitivity and specificity of quantitative enzyme-linked immunosorbent assay（ELISA） for ricin,30 kids of block agent were selected.The P/N showed that 1% caseinum+5% skimmed milk,5% skimmed milk+2% PEG20000 were both effective.Simultaneously,3 kinds of blocking condition were compared.The P/N showed that adding block agent to coated 96 plate with anti-ricin,then incubated for 1 hour in 37℃,achieved the best blocking effect.