Background Remimazolam is a novel, ultra-short-acting benzodiazepine used for general anesthesia. Because remimazolam is an emerging drug, the tolerance to remimazolam in benzodiazepine-taking patients has been unclear. Also, the efficacy of remimazolam in different races is not fully elucidated so far. Case presentation Here we experienced three cases in which high dose of remimazolam was needed for attempting to achieve appropriate anesthetic depth. Two of the three cases were of preoperatively benzodiazepine-taking patients. The other was a case of a Chinese patient. In all three cases, conversion to general anesthesia with propofol was necessitated. Conclusions When signs of inadequate sedative effect of remimazolam are observed in patients of benzodiazepine users or of different races, conversion to another sedative agent such as propofol should be considered.