The extracts from six algae species (Chaetomorpha linum and Caulerpa prolifera, Acanthophora sp. Gracilaria gracilis, Ectocarpus sp. and Cystoseira barbata) were tested for total phenols, total flavonoids and condensed tannin contents and for their in vitro antioxidant activities. The amount of total phenolics varied from 0.25 to 3.75 mg GAE/g, the amount of total flavonoids varied from 0.50 to 1.85 mg CE/g while the amount of condensed tannins varied from 0.50 to 3.40 mg CE/g. The acetonic extract of C. prolifera showed the highest total antioxidant capacity (16.42 mg GAE/g) as compared to C. linum (6.55 mg GAE/g DM), C. barbata (5.71 mg GAE/g), Ectocarpus sp. (4.91 mg GAE/g), G. gracilis (3.20 mg GAE/g) and Acanthophora sp. (2.62 mg GAE/g). In this study, only the acetonic extract of C. prolifera had a weak antiradical capacity against DPPH (IC₅₀ = 6.39 mg/ml). The acetonic extract of Ectocarpus sp. exhibited the highest β-carotene inhibitory activity (IC₅₀ = 1.62 mg/ml) as compared to C. prolifera (IC₅₀ = 3.42 mg/ml), C. linum (IC₅₀ = 5.58 mg/ml), C. barbata (IC₅₀ = 8.97 mg/ml), G. gracilis (IC₅₀ = 13.62 mg/ml) and Acanthophora sp. (IC₅₀ = 21.70 mg/ml). The evaluation of the iron chelating power of algae showed the absence of this activity with the exception of C. prolifera (IC₅₀ = 6.91 mg/ml). It can be concluded that these algae are promising natural products and more detailed investigations of their antioxidant properties and application possibilities are warranted.