In order to investigate the effects of different electron acceptors on the degradation of polycyclic aromatic hydrocarbons by Klebsiella sp. ZS1 under low-oxygen condition, the biodegradation ability was tested with the addition of three common electron acceptors, namely, 20 mmol/L Na₂SO₄,0 mmol/L NaNO₃, and 10 mmol/L FeCl₃. Low-oxygen condition (8% O₂) was controlled in a hypoxia station. The electron acceptor utilization and bacterial growth were measured by the national standard analytical methods; the remaining phenanthrene was determined by gas chromatography-mass spectrometry (GC-MS). Changes of the bacterial growth and the remaining phenanthrene were analyzed by one-way ANOVA. The results showed that ZS1 used SO₄2-, NO₃- and Fe3+ as electron acceptors at the utilization ratio of 74.7%, 0.2% and 4.5%, respectively. Meanwhile, the electron transfer rates were 1899、0.3663、7.679 μmol/d, respectively. Phenanthrene only decreased by 10.1% without inoculating ZS1. However, when ZS1 was inoculated, the degradation rates of no addition of electron acceptor and addition of SO₄2-, NO₃- and Fe3+ were 68.9%, 86.2%, 72.9% and 68.9%, respectively. The degradation rate constants determined using a first-order kinetic equation were 0.181,0.360,0.186 and 0.183 d-1. The bacteria growth with SO₄2- addition group was 2.5 times that of the control group, while the groups with addition of NO₃- and Fe3+ were similar to the control group, respectively. The results indicated that ZS1 can use SO₄2- and O₂ at the same time as its electron acceptor under low-oxygen conditions, while NO₃- and Fe3+ cannot be used. Furthermore, the addition of SO₄2- as an electron acceptor obviously stimulated the biodegradation of phenanthrene and the growth of the strain when compared to the control. However, the addition of NO₃- and Fe3+ had no statistically significant effect either on the reduction of phenanthrene or the growth of the bacterium.