Introduction: Kato-Katz is a laboratory method recommended by the Brazilian Ministry of Health (BMH) and the World Health Organization (WHO) as the gold standard for the diagnosis of human infection by Schistosoma mansoni. The method has great clinical and epidemiological relevance because it allows the parasite load quantification of the infected patient by calculating the number of eggs per gram (EPG) of feces. This classification may also be used to estimate the intensity of infection in the communities, to measure the impact of disease control measures, as well as to establish quality parameters for reading the slides. Objective: To describe the correct laboratory procedures for the parasitological diagnosis of S. mansoni infection by the Kato-Katz method based on the quality control protocol established by the Laboratory and Reference Service in Schistosomiasis/Centro de Pesquisa Aggeu Magalhães (CPqAM)/Fundação Oswaldo Cruz (Fiocruz)/BMH. Methods: We describe: 1) the technical steps for fecal sample preparation and reading the slides; 2) the technical limitations; 3) the standard operating procedure (SOP) to be adopted by laboratories; 4) the methodology for the internal and external quality control of the reading slides results; and 5) the tolerance limits accepted for such control. Conclusion: This study provides the laboratory which performs the diagnosis of schistosomiasis using the Kato-Katz method with parameters to implement a diagnostic service that can be evaluated internally and externally. The establishment of a quality protocol enables the comparison of data and the identification of failures in the operational procedure, which can be corrected by training personnel and taking actions for the problems identified.