BACKGROUND. As long ago times or perhaps longer, people were using insects as medicines for healing wounds, preventing infections and improving health. Some of these are purely anecdotal, while others have proven basis in fact as tested by modern medicine.Usage of insects intraditional medicine was recorded since time immemorial.Insects and their substances have been used as medicinal resources by different cultures since ancient time because of chemical compounds - e.g. pheromones, defensive sprays, venoms and toxins, which were sequestered fromplants or prey and later concentrated or transformed for their own use.In many parts of the world,different sections of the society have been using medico-entomological drugs to this day in their lives.A numberof studies has in recent years drawn attention to thetherapeutic value of certain species of insects, their products, and their developmental stages.As has been documented insects can be a source of drugs used in modern medicine, since compounds of insect origin can have immunological, analgesic, antibacterial, diuretic, anaesthetic and anti-rheumatic, antitumor properties. Numerous insect originated materia medicain Mongolian traditional medicine contribute this source of therapeutics and variety of ancientmedical treatises by local authors as well as translations of renowned Ayurvedic medical books about animals as medicine exist.Knowledge about therapy with insects in Mongolian traditional medicine is less studied even they have been used broadly since ancient time. Several orthodox practitioners have surveyed the therapeutic potentials of defensive agents in dark beetleknown as “stink beetle” in the past.Yet the scientific community has to give thismajor and crucial component of traditional Mongolian medicine the attention it deserves, scientific knowledge about biologically active principles within medicinal insect remain poorly unknown. AIM OF STUDY.To define chemical analysis of ethanol whole body extract of Tenebrionid beetles. METHOD AND RESULT. We collected Tenebrionid beetles from local regions including desert, grassland, and to make an 40% ethanol extract of whole body to determine species of Tenebrionid beetles by entomoscope. After 30 days for saving in organic extract, to determine chemical composition of filtered 2 ml sample solution by high performance liquid chromatography - mass spectrometry (HPLC-MS). Using digital usb microscope 2.0 mp to confirm special characters of Tenebrionid beetles to Tenebrionid B.miliaria in biological termin. In HPLC-MS, octadecanoic acid is presented in 2 regional samples. CONCLUSION. Octadecanoic acid, the surface lipid of the insect was determined from the ethanol whole body extract of Tenebrionid beetles.