Naphthalene-degrading bacteria can be isolated from volcanic mud that is rich in organic materials such as aromatic hydrocarbons. This study aims to isolate bacterial isolates capable of degrading naphthalene and to characterize the isolate using phenotypic and molecular methods. Isolation of bacterial isolates was carried out using enrichment technique in Bushnell-Haas (BH) medium added with 1 % (w/v) diesel fuel. A bacterial isolate DRK 9.1 was obtained from a mud sample in Renokenongo Village, Sidoarjo. The isolate was grown on Bushnell-Haas medium with the addition of 0.02 % (w/v) naphthalene and 0.5 % (w/v) yeast extract. Enumeration was carried out using the Total Plate Count (TPC) method and the degradation of naphthalene was investigated quantitatively by High Performance Liquid Chromatography (HPLC). The result revealed that isolate DRK 9.1 was able to grow in the medium with addition of 0.02 % naphthalene and 0.5 % yeast extract. An increase of total cell number was observed from 2.71x109 CFU/mL to 5.61x1010 CFU/mL after 24 h, followed by a decrease of total cell number to 2.83x1010 CFU/mL after 96 h. Results of HPLC analysis revealed that bacterial isolate DRK 9.1 reached 70.42 % naphthalene degradation after 24 h incubation and 99.59 % after 96 h of incubation. Bacterial characterization was carried out by phenotypic observation, biochemical test, and molecular method using 16S-rRNA gene. Results from phenotypic and biochemical characterization showed that the isolate DRK 9.1 belongs to member of the genus Pseudomonas. The isolate showed 99.64 % similarity to Pseudomonas aeruginosa JCM5962T.