Microalgae are organisms abundant in aquatic environments to be extremely tough. This feature is related to secondary metabolites produced by them, which at present are poorly studied, but may be of great interest to the pharmaceutical industry. In order to characterize chemically the microalgae Monoraphidium contortum, cultivation and the extraction process was performed, in addition, to qualitatively verify its bioactive compounds by analysis of secondary metabolites, to thereby correlate the antioxidant activity and the ability of cytotoxic species. The gathering was held at the fish pond on the property Rosa dos Ventos located in Fazendinha AP-district. The identification and selection were performed by microscopy and subsequently grown in the substrate rich in nitrogen, phosphorus and potassium (NPK) nutrients that allow the growth of these algae, with photoperiod and temperature controlled at 22ºC. The growth was evaluated daily and the extraction of the biomass was performed by maceration, using organic solvents of increasing polarity. The study of secondary metabolites M. contortum indicated the presence of phenols, tannins, and anthraquinones. M. contortum showed a significant antioxidant activity and got a low LC50, which resulted in low toxicity of the extracts. This species proved to be promising; this study emphasizes the importance of knowledge of the composition of bioactive compounds of species of microalgae as a source of the industrial application.