**Abstract**

This chapter will describe the antioxidant and biological activity of *Cissus sicyoides* and *Rosmarinus officinalis* leaf extracts, which represent an important natural source of antioxidants. These plants contain several bioactive compounds with high antioxidant activity, such as phenolic compounds, which are compounds that prevent or delay oxidative stress, acting as free radical scavengers (FRSs), and thus reduce the onset of cardiovascular disease, cancer, diabetes, epilepsy, stroke, among other diseases. The supercritical fluid extraction (SFE) has been studied to obtain antioxidant compounds from natural sources, without the drawbacks associated with conventional extraction processes, such as the use of organic solvents, which present toxicity and contaminate the extracts, is proposed.

**Keywords:** *C. sicyoides*, *R. officinalis*, antioxidant activity, biological activity, supercritical extraction
