A new bioreactor was designed to study the effect of aeration on biodegradation of phenanthrene in soil. The phenanthrene mixed previously with a little soil sample was added to the paddy soil sample in the reactor to make a phenanthrene concentration of 200 mg kg^-1. The sample was stirred frequently and allowed to equilibrate for two weeks. Six aeration rates were used in this experiment: 0, 0.02, 0.04, 0.06, 0.08 and 0.10 ³h^-1. Bioreactors were incubated at 25 and water content was adjusted to 60% of the water holding capacity (WHC). Changes of phenanthrene degradation rate, number of soil microbes, act ivity of polyphenol oxidase and soil pH were measured during the 60 day incubation. Results showed that aeration at 0.08 ³h^-1 had the highest phenanthrene degradation rate (72.6%). Compared to the control, the number of bacteria and fungi were significantly higher than that of the control. Aeration at 0.08 ³h^-1 also had the highest activity of polyphenol oxidase in soil. At this aeration rate, accumulation of acidic matter in soil was avoided and consequently soil pH remained constant which favored biodegradation of phenanthrene in soil. The high phenanthrene degradation rate achieved in the present study (when soil was aer ated at 0.08 m³h^-1) can be attributed to the increase in the quantit ies of bacteria and fungi in soil, the rise in the activity of polyphenol oxidase and rather stable soil pH. The new bioreactor can be further developed and used ex situ for rapid and efficient removal of organic pollutants in solid phase of soil.