Streptococcus agalactiae causes various severe infectious diseases such as sepsis, meningitis, and streptococcal toxic shock-like syndrome. Though Streptococcus agalactiae infection has been increasing recently, the comprehensive characteristic investigation of invasive Streptococcus agalactiae isolated in tertiary care hospitals has not been nearly performed in Japan. In this study, we investigated the clinical characteristics and antimicrobial susceptible patterns of 88 Streptococcus agalactiae isolated at two tertiary care hospitals during 2009-2015 in Japan. There was no significant differences between genders in our study. Two-third Streptococcus agalactiae were isolated from over age 60. Total mortality rate was 19% and invasive Streptococcus agalactiae-associated death cases have occurred every year after 2011. All Streptococcus agalactiae were completely susceptible toampicillin. Total non-susceptible rates of erythromycin, minocycline, levofloxacin and trimethoprim-sulfamethoxazole in this study were approximately 30%, 44%, 37%, and 7%, respectively. Our results suggest the need for continuous antimicrobial susceptibility survey of Streptococcus agalactiae.