Abstract: In order to explore the effect of Hemerocallis thunbergii Baker and its use in combination with Saussurea lappa, Coptis chinensis, Phellodendron amurense, area nut or pumpkin seed, experimental therapy was carried out on mice infected with schistosomiasis japonica. It was shown that when the drug or its complex was administered in the total dosage of LD₅₀, neither worm reduction nor dead worm was observed. Even when the animals were treated with Hemerocallis thunbergii in combination with tartar emetic, no beneficial effect was obtained. It was found that during the treatment, the worms decreased in size and depigmentation of the intestinal caeca followed. At the same time, the reproductive organs of the parasites degenerated obviously and after the treatment, most of the female worms were completely devoid of ova in their uteri. However, 7 days after the completion of the treatment, the worms completely recovered from the above-mentioned changes. The damage caused by Hemerocallis thunbergii on the host tissues consisted mainly of the softening of the white matter of the cerebro-spinal cord, while the neighbouring grey matter showed only a slight degeneration. Changes of the optic nerve are quite prominent. Cloudy-swelling of both hepatic cells and renal epithelium and hemorrhagic spots in the lung were observed.