Streptococcus acidominimus is rarely pathogenic in humans. In the literature, there are only few cases related to S. acidominimus, including pneumonia, meningitis, brain abscess, pericarditis, sepsis, and endocarditis. Up to now, only a few cases have been published on infective endocarditis due to S. acidominimus, commonly causing left-sided disease. Increasingly, it was noted that it is resistant to beta-lactams. There are no published cases of infective endocarditis due to S. acidominimus in Sri Lanka. Here, we report a case of right-sided native-valve infective endocarditis caused by S. acidominimus which was sensitive to beta-lactams in a 52-year-old man with congenital heart disease.