Methods of the creating systems for directional transport in the organism with the help of various carriers have recently been developed to improve the effectiveness and selectivity of the action of known drug substances (DS). Especially, the relevant problem is the toxicity reducing and selectivity increasing of antitumor DS. In recent years, studies are conducted on the creation of DS conjugates with natural polymers, in particular, with non-starch polysaccharides, many of which exhibit antitumor and immunomodulatory properties. Due to the unique combination of physico-chemical and biological properties, larch arabinogalactan (AG) is one of the most promising for the development of complex drugs with increased bioavailability and reduced toxicity.The aim of this work is to obtain mechanocomposites of cyclophosphamide (CPA) with the initial (molecular weight 16645 Da) and fragmented (molecular weight 8380 Da) arabinogalactan and to study their physico-chemical properties.According to IR and NMR 13C, 15N and 31P spectroscopy data, the long-term mechanochemical treatment does not lead to the change of the chemical composition of CPA molecules, only the formation of hydrogen bonds NH•••OH is observed. According to the data of X-ray diffraction analysis, IR and multi-nuclear NMR spectroscopy, the disordering of the crystal CPA structure and its molecular dispersion in the polysaccharide matrix without chemical interaction of the components are occurred during the mechanochemical treatment of CPA-AG mixtures at mass ratios of 1 : 5 and 1 : 10 for 4–12 hours.