Kalamiella piersonii is rare pathogen, and its pathogenicity to humans has been unknown. We describe an infant with bacteremia caused by Kalamiella piersonii. The patient was a 2-month-old girl presented with diarrhea, poor oral intake, and vomiting. The patient was tentatively diagnosed with acute enterocolitis. After admission, the patient developed a fever and blood culture yielded Gram-negative cocci, first determined to be Pantoea septica by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. However, genetic analysis of 16S rRNA allowed its identification as Kalamiella piersonii (GenBank accession number is OQ547240). Other housekeeping genes such as gyrB, rpoB, and atpD also identified the isolated strain as Kalamiella piersonii. The patient was successfully treated with cefotaxime without sequelae. Later, the patient was diagnosed as non-IgE-mediated gastrointestinal food allergy. Our experience indicated that Kalamiella piersonii is a potential human pathogen that can cause invasive infections even in infants and children. Identification of Kalamiella piersonii is difficult with routine conventional tests, and detailed studies including genetic analyses are necessary to clarify the pathogenicity of Kalamiella piersonii in humans.