Summary. -Rotavirus infection is the most frequent cause of infantile gastroenteritis worldwide and a signifi cant cause of death in infants and young children, following severe diarrhea and dehydration. Rotavirus vaccines are considered the most eff ective way to prevent rotavirus infections. In the process of developing rotavirus vaccines, it is crucial to establish a reliable and standardized method to determine vaccine titer. In this study, we developed an indirect immunofl uorescence assay (IFA) to determine the infectious titer of Lanzhou lamb rotavirus (LLR) vaccine grown in MA104 cells. Th e activating concentration of trypsin was 1 μg/ml for healthy monolayers of MA104 cells at 100% confl uence. Aft er incubation for 18 hr, a rabbit anti-SA11 polyclonal antibody, diluted at 1:800 in PBS, was added to all wells, followed by an Alexa-488-conjugated secondary antibody diluted at 1:500 in PBS. Cells were examined with a fl uorescence microscope. Our results show that IFA was more reproducible, more sensitive, simpler, and more rapid than the log 50% cell culture infectious dose-ELISA (lgCCID 50 -ELISA) in measuring the rotavirus vaccines. IFA provided a reliable basis for the qualitative and quantitative analysis of rotavirus, and the certifi cation of rotavirus vaccine production.Keywords: rotaviruses; diarrhea and dehydration; titration; indirect immunofl uorescence assay; lgCCID 50 -ELISA * E-mail: 732450624@qq.com; phone: +0086-18743024507. Abbreviations: CPE = cytopathic eff ect; CV = coeffi cient of variation; FCFU = fl uorescent cell forming units; IFA = indirect immunofl uorescence assay; lgCCID 50 -ELISA = log 50% cell culture infectious dose-ELISA; LLR = Lanzhou lamb rotavirus