The estrous cycle of rats is a four-day cycle consisting of proestrus, estrus, metestrus, and diestrus, which can be determined by analyzing the types of cells in vaginal smears. This study aimed to provide a fast and practical method for determining the estrous cycle phases in rats. Vaginal secretions from 30 female rats were collected daily for a month, and unstained material was observed under a microscope without the use of a condenser lens. Using a 10x objective lens, the proportion of three cell types—epithelial, cornified, and leukocytes—was analyzed. A 40x objective lens allowed for easier identification of individual cell types. The entire process, including collection, observation, and determination of phases, took 15-20 minutes. The study confirmed that the average estrous cycle duration is 4 days. The method is efficient and practical, suitable for use in various experimental protocols. It is particularly useful for beginners, as photomicrographs provided in the study aid in identifying the three cell types. The procedure should be performed with care to minimize stress and aggression in the rats, ensuring they become habituated to handling. The study also highlights the importance of considering the estrous cycle in experiments involving female rats, as it can influence hormonal responses and stress reactions. The findings support the use of vaginal cytology as a reliable method for determining estrous cycle phases in rats.The estrous cycle of rats is a four-day cycle consisting of proestrus, estrus, metestrus, and diestrus, which can be determined by analyzing the types of cells in vaginal smears. This study aimed to provide a fast and practical method for determining the estrous cycle phases in rats. Vaginal secretions from 30 female rats were collected daily for a month, and unstained material was observed under a microscope without the use of a condenser lens. Using a 10x objective lens, the proportion of three cell types—epithelial, cornified, and leukocytes—was analyzed. A 40x objective lens allowed for easier identification of individual cell types. The entire process, including collection, observation, and determination of phases, took 15-20 minutes. The study confirmed that the average estrous cycle duration is 4 days. The method is efficient and practical, suitable for use in various experimental protocols. It is particularly useful for beginners, as photomicrographs provided in the study aid in identifying the three cell types. The procedure should be performed with care to minimize stress and aggression in the rats, ensuring they become habituated to handling. The study also highlights the importance of considering the estrous cycle in experiments involving female rats, as it can influence hormonal responses and stress reactions. The findings support the use of vaginal cytology as a reliable method for determining estrous cycle phases in rats.