Phytase is one of the valuable industrial enzyme which is applied in the improvement of animal feed by providing non-organic phosphate. Increasing the phytase enzyme activity is commercially worthwhile. Using atmospheric pressure cold plasma is a strategy which could change protein activity by affecting their structures. In this study the effect of Helium plasma jet on phytase enzyme was investigated. For this purpose, phytase enzyme solution was treated with plasma in different time durations and enzyme activity was evaluated. The obtained results indicated the increase in enzyme activity which was positively related to the exposure time, and lack of pH effect on the trends of plasma treatment results.