Some of the most potent toxins are synthesized by fungi. Fungal toxins are the chemicals produced by fungi under certain conditions. They may be classified under different chemical classes. They are not essential for fungal growth or reproduction, but are toxic to plants, animals or humans. Fungal toxin contamination in certain agricultural commodities has been a serious concern for animal and human health. The major toxin-producing fungi are the species of Aspergillus, Penicillium, Fusarium and Alternaria. Aflatoxins, Citrinin, Fumonisins, Fusaric acid, Moniliformin, AAL-toxins, Alternariol, Ergot alkaloids, Ochratoxin A, and Zearalenone are some of the important fungal toxins responsible for causing economic losses to agriculture, spoilage of food that are often fatal to living systems. This research focuses on toxigenic fungi, toxins and their characteristics with biological effects.