In this report,methods for preparing magnetic iron-dextran particles and separating highly synchronized (95%) ciliate conjugating pairs are introduced.When iron-dextran particles are added to the mixtures of complementary mating types of ciliates,single cells and loose conjugating pairs form food vacuoles containing the iron-dextran particles while absent from the tight mating pairs.By applying magnetic force,single cells and loose mating pairs can be removed from the tight conjugating pairs.This method has several advantages: simplicity,speediness,high quality,universality and practicality.No negative effects have been found when perform the experiments by this method.