Investigation of species composition of aquatic invertebrate in Pu Luong Nature Reserve, Thanh Hoa province has given a total of 33 zooplankton species belonging to 20 genus of 15 family, 2 phylum. Of these, Rotatoria is the highest with 21 species occupying 63.64 percent belonging to 10 genus, 7 family. Next is the Cladocera with 10 species-30.3 percent belonging to 9 genus, 6 family and the Copepoda with 2 species-6,06 percent belonging to 2 genus, 2 family. The survey of zoobethic fauna yielded 51 species belonging to 42 genus, 3 phylum (Annelida, Arthropoda, Mollusca). Of these, Arthropoda is the highest with 28 species occupying 54.9 percent. Next is the Mollusca with 22 species-43,14 percent and the Annelida with 1 species-1.96 percent. Analyses of the Shannon-Wiener index (H') showed that the diversity index (H') varies from 1.38 to 2.88 on zooplankton and from 1.38 to 3.24 on zoobenthos.