The number of diabetics is rapidly growing every day in all parts of the world. By the year 2010, the number of patients suffering from diabetes had amounted to more than 230 million people, which is estimated as 3.5% of the whole world adult population . According to expert forecasts, this number is projected to double by the year 2025, which is going to be 7% of whole Earth population. It was calculated that every 10 seconds someone in the world dies due to diabetes and its complications, which is 3 million people per year. The average life expectancy of children with diabetes is less than 28.3 years of onset. Diabetes is considered to be the fourth most common cause of death in industrialized countries. Vascular complications due to diabetes cause early disability and high mortality. Mortality from heart diseases and strokes is 2-3 times more likely for patients suffering from diabetes, whereas blindness, nephropathy and lower limbs gangrene happen respectively 10, 12-15 times, and almost 20 times more often for diabetics than general population. The number and strength of complications depend directly on the blood glucose level control quality. At the moment, the blood glucose level measurements are performed by glucometers [2,3]. This method requires that a patient makes a finger puncture for every measurement. About five punctures per day should be done for proper glucose monitoring, which is about 1,800 punctures per year. Besides, each measurement by glucometer requires a distinct test strip. Expenses for 1,800 test strips could be estimated as about 450 euros per year. It is also necessary to take into account that each puncture has a risk of blood poisoning. Using non-invasive techniques for glucose level control could reduce the amount of possible risky manipulations by 1800 per year. Moreover, it is worth mentioning that only eight of ten fingers are suitable for puncturing, and the constant skin damage which cannot be avoided is quite annoying for the patients. Most biomolecules have characteristic signature frequencies in the terahertz (THz) range, which can reveal their presence and determine the concentration. Therefore, this paper is intended to study the blood optical properties in the THz frequency range in order to determine THz radiation effect on blood. The main aim of this investigation is to determine the effect of blood glucose concentration on the blood optical properties. In the case if blood optical properties vary at different glucose concentrations having a proportional relationship between them, these results will confirm the possibility of development of non-invasive procedures for blood glucose level diagnostics.