The potential of algae, plants, fungi, and bacteria to produce a wide spectrum of volatile organic compounds (VOCs) including terpenes, alkanes, alkenes, alcohols, ketones, aldehydes, benzenoids, esters, and sulfo compounds is remarkable. Thus, the antifungal activity of volatiles emitted from D. tharense, C. vulgaris, and N. arenaria was evaluated against M. phaseolina and F. oxysporum under living conditions through a system that allows the exchange of VOCs between algae and phytopathogenic fungi without physical contact between them. Volatiles released from C. vulgaris and D. tharense cultures cause a significant growth reduction for F. oxysporum and M. phaseolina, and the highest activity was recorded by C. vulgaris. Volatiles of C. vulgaris which exhibited the highest antifungal activity were collected under natural living conditions by the headspace method and analyzed by GC/MS. GC/MS analysis of C. vulgaris volatiles proved that a complex mixture of bioactive and inactive natural compounds was produced by this alga. The identified compounds produced by C. vulgaris cells were belonging to different chemical classes, such as alkanes, cyclic alkanes, phenols, halogenated compounds, amides, acids, alcohols, ketones, lactones, fatty esters, fatty acid methyl esters, phthalic acid derivatives, and alcohols. The antifungal activity of C. vulgaris is attributed to the synergetic effect of all potent antifungal compounds produced by the alga cells.