A new mouse ASF-LL model of adult T-lymphoma/leukemia (ATLL) in humans was characterized by cytological, histopathological, and flow cytometry analyses. Encouraging similarities of morphological, pathological, and clinical signs were found. These included characteristic flower appearance of leukemic cells, lymphadenopathy and hepatosplenomegaly, multiple growths in the skin, urogenital tissues, lungs and pituitary gland, CD4+CD25+ phenotype of the majority of tumor cells that were selectin-L positive, a rapid clinical course, and poor response to standard chemotherapy. Plant peptides obtained from the traditional Russian herbal medicine have gradually gained considerable attention as a new source of anticancer drugs. We have tested antitumor activity of a peptide extract PE-PM obtained from a mixture of Chelidonium majus L., Inula helenium L., Equisetum arvense L. and Inonotus obliquus in new mouse T-lymphoma/leukemia model ASF-LL. Distinct antitumor activity of two local injections of the peptide extract PE-PM was detected by tumor growth inhibition and survival improvement of 33% of recipients bearing intraperitoneal form of ASF-LL.