Abstract: Biological effect of pHvalues were tested for 24-96 hours to five species of leeches (Hirudinea)Glossiphonia lata, Erpobdella octoculata, Whitmania laevis, Whitmania acra nulata and Hirudo nipponia in Wuchang using bioassay method. The results indicate:3 species(Whitmania laevis, Whitmania acranulata and Hirudo nipponia)in rice fields are more sensitive to the variation pHvalues thanspecies (Erpobdella octoculata and Glossiphonia lata)in the water near lakeside, among them, Whitmania acranulata has the highest sen sitivity(pH6.0-7.2), Erpobdella octoculata has the widest enduring limit(pH 4.0-10.5); as pHvalue raised to 9.5, the percentage of mortality of 3 species in rice fields reached 40% or more, among them, Hirudo nipponia was 70%; as pHvalue dropped to 3.0, 2 species in the water near lakeside all died in24 hours, but Hirudo nipponia only had the mortality of 10%.

Key words: Leech, pH value, Enduring limit, Sensitivity