To compare the acute toxicity of the decocted water solution of Sargassum, Radix Glycyrrhizae, the prepared Radix Glycyrrhizae, the Sargassum with Radix Glycyrrhizae, the Sargassum with the prepared Radix Glycyrrhizae, the Haizao Yuhu decoction (Radix Glycyrrhizae) and the Haizao Yuhu decoction(the prepared Radix Glycyrrhizae) in mice, the water extraction components of different groups were prepared, and comparisons were made in accordance with the classical acutetoxicity test methods. The LD₅₀ of the Sargassum water extraction is 35.67g·kg^-1·d^-1, the water extraction of the Sargassum with the prepared Radix Glycyrrhizae is 44.29g·kg^-1·d^-1and the water extraction of the Sargassum with the Radix Glycyrrhizae is 50.98g·kg^-1·d^-1, which are equal to, respectively, 145.2 times, 182.6 times and 211.5 times of 70kg adult's daily dried medicinal herb intake. In the experiment of LD_50(n), the death rate of the prepared Radix Glycyrrhizae reaches 50 % by the end of consecutive 8 days, and its LD₅₀₍₈₎ is 70.69g·kg^-1·d^-1.The LD₅₀₍₁₉₎ of the Radix Glycyrrhizae is 82.98g·kg^-1·d^-1; the LD₅₀₍₇₎ of the Haizao Yuhu decoction (Radix Glycyrrhizae) is 79.24g·kg^-1·d^-1; the LD₅₀₍₆₎ of the Haizao Yuhu decoction (the prepared Radix Glycyrrhizae) is 77.49g·kg^-1·d^-1. The acute toxicity of different groups in mice is: Sargassum > Sargassum with the prepared Radix Glycyrrhizae > Sargassum with Radix Glycyrrhizae > prepared Radix Glycyrrhizae > Haizao Yuhu decoction (the prepared Radix Glycyrrhizae) > Haizao Yuhu decoction (Radix Glycyrrhizae) > Radix Glycyrrhizae. However the toxic substances, the toxicity characteristics, and the toxicity mechanism are not yet entirely clear, and they should be further studied.