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Laccase (benzenediol: oxygen oxidoreductase), is a multicopper polyphenol oxidase enzyme which has glycoprotein structure. The Researches are indicated that laccase enzyme can play role in detoxification of aromatic pollutants (as petroleum derivatives) and conversion them to less toxic compounds. On the other hand, because of its extensive, fibrous root system; Festuca arundinacea, creates an appropriate environment that causes increased catalysis of petroleum contaminants. Considering the fact that increasing in catalysis of pollutants can be provided by presence and changes in activity of various plant enzymes, in this research; the changes in laccase activity of Festuca's vegetative organs under soil pollution with different concentration of diesel fuel has been investigated. For this purpose, at first, the seeds of Festuca were cultivated in pots containing diesel fuel polluted soils and also control pots in greenhouse conditions. Then in specified time treatments, plants were harvested and plant extract containing laccase were extracted from aerial parts and roots of the plant, separately. After doing centrifuge, changes in enzyme activity were calculated by spectrophotometer. The results show that creation of soil pollution treatments compared with control samples, leads to increase in laccase activity in many cases. In other words, by increasing in laccase activity, the plant will increase its potency of decomposition and assimilation of pollutant hydrocarbons.