Oysters are filter feeders that bioaccumulate bacteria in water while feeding. To evaluate the bacterial genomic DNA extracted from retail oyster tissues, including the gills and digestive glands, four isolation methods were used. Genomic DNA extraction was performed using the Allmag™ Blood Genomic DNA (Allrun, Shanghai, China), the MiniBEST Bacterial Genomic DNA Extraction kits (Takara, Dalian, China), and the phenol-chloroform and boiling lysis methods. The concentration of the genomic DNA was measured using a spectrophotometer. The purity of the genomic DNA was evaluated by PCR amplification of 16S rDNA followed by determining the cloning efficiency of the amplicon into the pMD19-T vector. Furthermore, the bacterial DNA quality was also evaluated by PCR assays using a pair of species-specific primers for Vibrio parahaemolyticus. Our results showed that the two commercial kits produced the highest purity of DNA, but with the lowest yields. The phenol-chloroform method produced the highest yield although it was time-consuming. The boiling lysis method was simple and cost effective; however, it was only suitable to isolate genomic DNA from bacteria present in retail samples following an enrichment step. The two commercial kits were good candidates for genomic DNA extraction from retail oyster tissues without enrichment.