Abstract: Micro-electrophoreses are analytical techniques available for separating and characterizing RNAs, DNAs and proteins extracted from small amounts of biological materials. Microisoelectric focussing, one kind of micro-electrophoreses, is used for the first time to analyse esterase isozyme of the wild ciliate Carchesiurn polypinum(Linne, 1758), the isozymes of which have not been investigated before. The results of the experiments demonstrate: 1, samples of two colonies of Carchesium polypinum(about 200 zooids) are sufficient for the microfocussing analysis of esterase isozyme; 2, Carchesiurn polypinum separated immediately from the sample collected from Lake Donghu has almost the same pattern of esterase isozyme as the sample which has been kept in the laboratory for 10 hrs at 30℃. Therefore, isozymes of wild ciliates can be analysed by microfocussing.