Background/Aim. The inhibition of factor Xa (FX) by the use of low-molecular heparin (LMH) is important clinical procedure in patients with moderate and high risk for the developament of venous thromboembolism (VTE) and pulmonary embolism (PE). The aim of this study was to determine the level of inhibition of FXa by the use of prophylactic doses of LMH nadroparin-calcium and reviparine-sodium which were applied in urological patients with moderate risk for VTE and PE. Methods. The examination included 80 urological patients divided into 4 groups after urological, uroradiological and anesthesiological preoperative preparation and categorization of anesthesiological risk according to the ASA III classification. The first two groups, of 20 patients each, received the recommended doses of LMH in accordance with the preoperative risk, and an inhibition of FXa 48 hours after the surgical operation and four hours after the administration of LMH was determined. Heptest and homogenous anti-Xa test were used for monitoring of FXa inhibition. Since the obtained anti-Xa values were not satisfactory, two more groups were formed and given double the recommended doses. In these new groups, inhibition of FXa was in recommended range. Standard descriptive statistical parameters were used for describing the charateristics of the people from the formed groups. Results. All the patients examined were clinically estimated as patients of moderate risk, for VTE and PE. There were no statistically singificant difference in body weight of the patients who received nadroparin-calcium 0.3 ml and reviparine-sodium 0.25 ml and those who received their double doses, respectively. The level of FXa inhibition in the group in which the dose of nadroparin-calcium of 0.6 ml was applied was statistically significantly higher than in the group which received the dose of 0.3 ml (Mann-Whitney U test: Z = 5.416; p < 0.0001). The level of FXa in the group given reviparine-sodium 0.5 ml was significantly higher than in the group which received the half of this dose (Mann-Whitney U test: Z = 5.416; p < 0.0001). This research did not confirm a statistically significant difference in the levels of FXa inhibition in patients who received nadroparincalcium as VTE and PE prophilaxis in the dose of 0.6 ml and those who received reviparin-sodium 0.5 ml (in two doses of 0.25 ml) (Mann-Whitney U test: Z = 0.163; p > 0.05). Conclusion. According to biochemical monitoring, the recommended doses of LMH are insufficient for the prophylactic inhibition of FXa in urological pateints with moderate risk for VTE and PE, so the higher doses which inhibit FXa are recommended. .