Fecal microbiota transplantation (FMT) by manual preparation has been applied to treat diseases for thousands of years.However,this method still endures safety risks and challenges the psychological endurance and acceptance of doctors,patients and donors.Population evidence showed the washed microbiota preparation with microfiltration based on an automatic purification system followed by repeated centrifugation plus suspension for three times significantly reduced FMT-related adverse events.This washing preparation makes delivering a precise dose of the enriched microbiota feasible,instead of using the weight of stool.Intraperitoneal injection in mice with the fecal microbiota supeatant obtained after repeated centrifugation plus suspension for three times induced less toxic reaction than that by the first centrifugation following the microfiltration.The toxic reactions that include death,the change in the level of peripheral white blood cells,and the proliferation of germinal center in secondary lymphoid follicles in spleen were noted.The metagenomic next-generation sequencing (NGS) indicated the increasing types and amount of viruses could be washed out during the washing process.MetaboIomics analysis indicated metabolites with pro-inflammatory effects in the fecal microbiota supeatant such as leukotriene B4,corticosterone,and prostaglandin G2 could be removed by repeated washing.Near-infrared absorption spectroscopy could be served as a rapid detection method to control the quality of the washingprocess.In conclusion,this study for the first time provides evidence linking clinical findings and animal experiments to support that washed microbiota transplantation (WMT) is safer,more precise and more quality-controllable than the crude FMT by manual.