The current study aimed to use the biological treatment (Phycoremediation) for sewage water, where the green alga Chlorella vulgaris was used in the treatment process and to improve water quality by removing some of the pollutants contained in the water, the most important of which are hydrocarbon pollutants, and to note the changes in the biochemical properties of the algae, such as the SOD enzyme And CAT enzyme and total chlorophyll before and after the treatment process. The treatment process took place between wastewater and green algae when the latter reached a stable stage to ensure its high treatment capacity and the best possible life span. Where the measurements were made for the characteristics of the treated water in addition to the biochemical measurements of the algae on the 4th and 8th day of the biological treatment. A study of the growth curve of C. vulgaris showed that the growth phase started on day 6, reached stability on day 12, then reached the death phase on day 19, and continued to decline until the death of the alga. The results of the study showed the value of what was contained in the wastewater before the treatment process, as it was as follows: total hydrocarbons (5.38 mg / L), as for the biochemical properties of algae before exposure to wastewater, they were as follows: Superoxide dismutase enzyme (1.2197 U / mg), catalase enzyme ( 0.6023 U/mg), total chlorophyll (6.1503 mg/g). After the wastewater treatment process was completed, the high ability of green algae to remove hydrocarbon pollutants from the water was shown, at a rate of (72.3% - 64.5%), respectively. The results of the study showed the effect of sewage water on some physiological characteristics of algae, as it showed an increase in the activity of SOD after 4 days of treatment to reach (1.33 U / mg), while the activity decreased on the 8th day to reach (1.289 U / mg), as for the CAT enzyme It appeared in the same way as the previous enzyme, as its effectiveness increased after 4 days of treatment to reach (0.6916 U/mg), and decreased on the last day to reach (0.5476 U/mg).