We applied length polymorphism (LPM) of PCR-amplified DNA fragments from the 16S ribosomal RNA gene (16S rDNA) to analyze bacterial communities in soil. The PCR (polymerase chain reaction) primers were designed to classify soil bacteria into three groups: 1) the α and δ subclasses of Proteobacteria, 2) the β and γ subclasses of Proteobacteria, and 3) the flexibacter and Gram- positive bacteria. Eight variable regions of 16S rDNA were analyzed, and as a result, region 1 of 16S rDNA was found to be effective for LPM analyses. Bacterial DNA was extracted directly from the soil samples, and the LPM patterns for the PCR-amplified DNA fragments were obtained using a high- resolution gel. We observed substantial changes in the LPM patterns, which were attributed to the changes in the vegetation and to seasonal changes. These changes showed that the proposed technique can be applied for monitoring changes in bacterial communities.