Abstract: A previous article relating to the ecological study on the planktonic protozoans inLake Dong Hu (Tung-Hu) was published in 1965. The present paper deals with theperiphytic protozoans of the same lake. Samples were collected at semi-monthly in-tervals at 2 stations (Stations Ⅳ and Ⅴ in Fig. 1) during the period from December,1963 to December, 1964. Examination of the samples revealed tt total of 175 speciesof periphytic protozoans (Table 2), of which 110 species were designated as euperi-phyton and the remaining 65 species as pseudoperiphyton. Since only 27 species werecommon to both planktonic and periphytic habitats, the species composition of theperiphytic protozoans was radically different from that of the planktonic ones. Regarding the seasonal fluctuation in the abundance of periphytic protozoans thatgrew on the predominant macrophytes (Potamogeton maackianus, Myriophyllum spica-tum and Ceratophyllum demersum), the maximal number was recorded at relatively lowwater temperatures (Figs. 3-4). The occurrence of this maximum was mainly dueto the extraordinary richness of the most predominant species, Vorticella campanula,comprising 80-90% of the sum total of periphytic protozoans (Fig. 5). Centropyxisspp., which attached mainly to the leaves of Potamogeton maackianus, constituted thenext predominant group, possibly because of the precipitation of calcium carbonate,which is so needful to this group in building up the lorica, by the process of phytosyn-thesis in this plant. In order to elucidate the discrepancy between the season of maximal abundance(winter) of the periphytic protozoans on the one hand and that of the planktonic ones(spring and autumn) on the other hand, a parallel test by means of artificial substra-tum was made during the investigation. It has been demonstrated that while thespecies composition of periphytic protozoans on the glass slides was essentially the sameas that on the aquatic macrophytes, the tempo of colonizing in the case glass slides was,however, most swift in August and September. From an analysis of the interrela-tionship between the seasonal fluctuatuons in the abundance of protozoans growing onCeratophyllum demersum, the biomass of the plant, and the abundance of protozoansattaching to artificial substratum (Fig. 10), it seems justified to suggest that the lifecycle of the macrophyte itself exerts a strong influence over the seasonal fluctuatuonin the abundance of periphytic protozoans. The role of the periphytic protozoa as it biological indicator for estimating thedegree of saprobity was also investigated. That the annual average number of periphy-tic protozoans on the leaves of Myriophyllum spicatum at Station Ⅳ was 4.5 times that of Station Ⅴ (Table 1) has been in conformity with the results of our previousstudy on the planktonic protozoans. In conclusion, the author points out that both theperiphytic and planktonic protozoans, especially the attached peritrichous ciliates, playan important role in the assessment of saprobity levels. The new species earmarkedin Table 2 will be described in a separate paper.