Abstract: To further confirm whether similar hormone in the high animal could exist in the protozoa, the research was conducted with the distribution of Rabbit Anti-human Prolactin using the immunocytochemical staining technique in Stylonychia mytilys under optical microscope. The results indicated that pellicle, cirri, adoral zone membranelle (AZM) and undulating membrane (UM) of Stylonychia mytilys were heavily stained and thickly distributed, but cytoplasm were lightly stained and densely distributed. Macronuclei reactions were negative. This was in accordance with the localization of neuropeptide substances in Stylonychia mytilys. That was generally consistent with combining sites of different first antibodies. Because they had not still differentiated or differentiated incompletely, the substances regulating vital movement were still in primary form so that they could took on positive reaction with kinds of antibodies.