Abstract: Al₂O₃ can be used for the purification of liquid scintillator, but radioactive contamination may happen in the process of purification. Radioactive contamination of liquid scintillator in the process of purification is studied in this paper. Research shows that when the Al₂O₃ was mixed with liquid scintillator, the supernatant liquid scintillator can be contaminated by radioactive impurities in the suspended Al₂O₃. The results of liquid scintillator filtration experiments with Al₂O₃ filter column show that contamination of liquid scintillator may come from the radon in air. The Al₂O₃ filter column can prevent most of the radioactive impurities from flowing into the liquid scintillator with fine Al₂O₃ particles. After the removal of the influence of radon, there is no significant difference in radioactivity between filtered liquid scintillator and unfiltered liquid scintillator in the range of standard deviation. In other words, the radioactive contamination of liquid scintillator from Al₂O₃ is below detection sensitivity of liquid scintillation counter.