Abstract: The effect of different concentrations of NaCl (0-5%) on biodegradation of aliphatic fractions of crude oil in polluted soil has been studied. The relative contribution of volatilization and biodegradation of crude oil and its aliphatic fractions in crude oil-contaminated soil during four months has been investigated. The crude oil reduction was about 12, 41 and 15% in 5% NaCl, 0% NaCl and non-aerated samples, respectively. The reduction ratios of C17 to pristine and C18 to phytane, as indices of biodegradation, were 75 and 73% in 0% NaCl sample, 28 and 31% in 5% NaCl sample and 46 and 51% in non-aerated sample, respectively. Total aliphatic reduction four months after crude oil contamination was 29 and 7.3% in 1% NaCl and 5% NaCl, respectively. Present results indicated that the presence of NaCl attenuated the oil reduction process presumably through its inhibitory effect on bacterial growth. Increasing NaCl concentration reduced biodegradation rate. We also found biodegradation was the main factor in elimination of crude oil and its aliphatics fraction reduction in comparison to volatilization. We conclude that aeration and removal of NaCl from the contaminated soil are useful approaches in oil removal from contaminated soil.