Naphthalene is a polycyclic aromatic hydrocarbon (PAH) pollutant that can be found in the environment. Naphthalene removal can be attained by biodegradation using bacteria. Volcanic mud contains organic materials including PAH, can support the growth of hydrocarbon degrading bacteria. Bacterial strain Pseudomonas aeruginosa DRK 9.1 was isolated from volcanic mud in Renokenongo Village, Sidoarjo. The objective of this research was to determine the capability of P. aeruginosa DRK 9.1 to degrade naphthalene with the addition of glucose as the growth stimulant. P. aeruginosa DRK 9.1 was grown in Bushnell-Haas medium with addition of 0.02 % (w/v) naphthalene and 0.5 % (w/v) glucose. Enumeration of the bacterial cells was performed using Total Plate Count (TPC) and quantitative determination of naphthalene degradation used High Performance Liquid Chromatography (HPLC). The results presented that the cell total number increased from 6.18 × 109 CFU/mL to 2.10 × 1011 CFU/mL after 24 h incubation. After 96 h incubation, the cell number decreased to 3.32 × 1010 CFU/mL. The results of naphthalene biodegradation by HPLC showed that naphthalene concentration decreased by 40.85 % and 82.47 % after 24 and 96 h incubation, respectively.