Provided are an oligonucleotide primer set for amplifying at least one target sequence of the 16S rRNA gene in gram-negative bacteria and at least one target sequence of the 16S rRNA gene in gram-positive bacteria, a probe set specifically hybridizing with at least one target sequence of the 16S rRNA gene in gram-negative bacteria and at least one target sequence of the 16S rRNA gene in gram-positive bacteria, a microarray comprising the probe set, a method of discriminating gram-negative bacteria and gram-positive bacteria, and a kit for discriminating gram-negative bacteria and gram-positive bacteria, including the primer set.