Modern trends in the oil refining industry development are caused by the quality deterioration of oil produced, on the one hand, and the growth in the demand for motor fuel, on the other hand. As a result, crude oil with high contents of sulfur, nitrogen, and metals is processed. To process such raw materials and to produce high-quality light oil products, catalytic hydrogenation processes are used with compounds of transition metal (in particular, nickel, cobalt, molybdenum, and tungsten) as catalysts [1]. In this work, the catalytic activity of 5-phenyl-3[2-(thiazol-2-yl)hydrazono]-3H-furan-2-one Co(II) during diesel fraction hydrotreatment was studied. The cobalt complex of the substituted furan-2-one obtained by method described in [2] was deposited onto γ-Al2O3 by impregnation. The activity of the resulting catalytic system was studied during diesel oil fraction hydrotreatment in a flowthrough type plant within 320–380°C with a step of 20°C at a hydrogen feed rate of 6 L per h. Preliminary, our catalyst was activated in a hydrogen flow for 2 h. The duration of the experiment was 1 h, the feed rate was 6 mL per h. The main indicator of the activity of the catalytic system was the hydrodesulphiding ability, i.e. the degree of purification of raw materials from sulfur-containing compounds. By the difference in the sulfur content in the diesel fraction before and after our experiment, the degree of purification of the diesel fraction at several process temperatures was estimated. The sulfur concentration was determined by burning the oil product in an air jet and trapping the formed sulfur dioxide and trioxide by solutions of hydrogen peroxide with sulfuric acid with subsequent titrating with sodium hydroxide solution. As a result of our study, it was shown that our catalytic system began to function already at 320°С (the purification degree 45%), however, the best result was achieved with a feed rate of 0.6 h-1 and a temperature of 360°C, the purification degree being 75%.