Corynebacterium simulans was first reported in 2000. Its characteristics such as isolation frequency, specimen types, and antimicrobial susceptibilities are poorly understood, because identification is difficult using conventional methods. We performed a retrospective observational study of 13 and 317 strains of C. simulans and C. striatum, respectively, isolated from consecutive patients at Nagoya University Hospital from January 2017 to December 2018. We analyzed patients' backgrounds, types of specimens, and antimicrobial susceptibilities. Antimicrobial susceptibilities were compared with those of C. striatum. The frequencies of isolation of C. simulans and C. striatum were 3.9% and 96%, respectively. C. simulans was not detected in specimens associated with mucous membranes, such as sputum and secretions from the craniocervical region, which were frequent for C. striatum. C. simulans was mainly detected in the skin (61.5%). All C. simulans isolates were susceptible to anti-MRSA drugs, as well as to numerous other antibiotics, including those that are orally administered. For example, C. simulans was significantly more susceptible to penicillin G, ceftriaxone, and ciprofloxacin than C. striatum (respective susceptibilities: 66.7% vs 5.4%, 50.0% vs 4.0%, 66.7% vs 5.9%). There was no significant difference between meropenem and erythromycin, although susceptibility to each was relatively high (100.0% vs 31.7%, 50.0% vs 11.9%). C. simulans was susceptible to numerous orally administered antibiotics and more susceptible to antimicrobial drugs than C. striatum. C. simulans was detected less frequently than C. striatum and was infrequently detected in specimens associated with mucous membranes. These characteristics will aid the selection of optimal antimicrobial therapies.