The seasonal changes of bacterial community composition in the scallop culture area of Liuqinghe Bay in Qingdao were analyzed in this study.Five liters of water samples from the 0.5 m depth were collected each time every month from May 2009 to April 2010,except February,and the one liter water samples were filtered by sterilized micro-filtration membranes to collect the micro-organisms within the size of 0.22 μm to 3.00 μm.Total DNA of the samples were extracted by CTAB method,the bacterial 16S rDNA V3-V5 variable sequence was amplified by PCR,the amplified sequences were separated by DGGE(denaturing gradient gel electrophoresis)techniques,and the DGGE fingerprint was analyzed by software Quantity One.Totally,36 bands with different positions were showed.The most abundant bacterial composition was found in January,and the least was found in March.Based on the the UPGMA cluster analysis,the monthly samples were grouped into 2 seasonal types:March to May,June to January.A total of 20 dominant DGGE bands were successfully cloned and sequenced.Blast results showed that the similarities between these cloned sequences and the sequences in the GenBank were all over 94%.The 20 bands belonged to α-Proteobacteria,β-Proteobacteria,γ-Proteobacteria,Bacteroidetes,Actinobacteria,and Verrucomicrobia,respectively.