The pharmaceutical interest in marine organisms had increased in the early 1950's since the discovery of unusual sponge nucleosides which were the basis for the first marine–derived anticancer agent Ara-C. An extensive literature survey was carried out on marine sponges and their unique metabolites in the last two decades. Almost none of these studies had characterized the redox-activities of sponges' crude extracts neither their metabolites and just a few of them discussed the implications of free radicals in their findings. Although Brazilian's Coast is 8.000 km longer, poor research had been performed on this enormous promising resource. At this perspective, the aim of this study was screen the redox-activities of the aqueous extracts of Mycale arcuiris, Tedania ignis and Guitarra sepia, collected at Reserva Biológica Marinha do Arvoredo, SC, South Brazil. Different in vitro radical producing systems were used to perform this investigations. So, 10, 25, 50 e 100 mg/mL of the aqueous extracts were evaluated by: 2-deoxyribose oxidation by ^·OH, nitrite production by NO e lipid peroxidation by TBARS. The data was submitted to one-way ANOVA and Duncan´s test post hoc and difference was significative when p<0.05. At 10 and 25 mg/mL concentrations M. arcuiris extract increased nitrite production while protected lipid from peroxidation. T. ignis extract increased nitrite production at 10 and 25 mg/mL and increased lipid peroxidation at 10, 25 and 50 mg/mL. G. sepia extract increased either nitrite production at 10 and 25 mg/mL and lipid peroxidation at 10, 25 and 50 mg/mL. But at 25, 50 and 100 mg/mL were able to avoid lipid oxidative damage until 30%. All tested concentrations of the three aqueous sponge extracts were able to increase the 2-deoxyribose degradation by ^·OH. Considering that generation of free radicals is part of cellular defense system and is intended to destroy invading microorganisms and other cells, our findings suggest that sponges have the potential to provide future drugs against important diseases modulated by reactive species, such as cancer. Nevertheless, further investigation is needed to confirm the exact mechanism observed in our findings.