Objective: We reviewed the clinical data of 78 patients who underwent maintenance hemodialysis in Asan Medical Center from April 1 to May 31, 2021. We retrospectively collected demographic and laboratory results including platelet, prothrombin time, activated partial thromboplastin time, fibrinogen, d-dimer, and anti-PF4 antibody. Methods: Twenty patients (25.6%) were vaccinated with ChAdOx1 nCov-19. Baseline platelet count of the vaccinated patients was 148.40±49.61 x103/mm3, and it slightly increased to 156.90±48.63 x103/mm3 three weeks after the vaccination (p=0.199). In patients with baseline platelet count < 150 x103/mm3 (n=9), platelet count increased by 19% on average from baseline to three week after vaccination, from 100 x103/mm3 to 119 x103/mm3. However, there was no change of platelet counts in patients with baseline platelet count > 150 x103/mm3 after vaccination or the unvaccinated patients. (table 1) The PT, fibrinogen and d-dimer in the vaccinated patients did not show significant differences, and aPTT was slightly decreased but in normal range, when we compared the figures of one week and three weeks following the vaccination. (Table 2) When the vaccinated patients were divided by baseline platelet count (more or less than 150 x103/mm3), there was no difference for coagulation factors between divided groups. Anti-PF4 antibody tests, which were performed three weeks after the vaccination, were negative in the all vaccinated patients. Results: The vaccination with ChAdOx1 nCov-19 did not cause significant influence on platelet and coagulation factors in hemodialysis patients. The results for anti-PF4 antibody tests also did not show the risk and possibility of VITT. The vaccination for hemodialysis patients would be safe modality to prevent COVID-19 infection. Conclusions: Objective: The COVID-19 pandemic is more lethal for patients with underlying disease, so it is necessary for hemodialysis patients to get vaccinated. We observed the changes of platelet and coagulation factors in hemodialysis patients who received ChAdOx1 nCov-19 vaccine. Methods: We reviewed the clinical data of 78 patients who underwent maintenance hemodialysis in Asan Medical Center from April 1 to May 31, 2021. We retrospectively collected demographic and laboratory results including platelet, prothrombin time, activated partial thromboplastin time, fibrinogen, d-dimer, and anti-PF4 antibody. Results: Twenty patients (25.6%) were vaccinated with ChAdOx1 nCov-19. Baseline platelet count of the vaccinated patients was 148.40±49.61 x103/mm3, and it slightly increased to 156.90±48.63 x103/mm3 three weeks after the vaccination (p=0.199). In patients with baseline platelet count < 150 x103/mm3 (n=9), platelet count increased by 19% on average from baseline to three week after vaccination, from 100 x103/mm3 to 119 x103/mm3. However, there was no change of platelet counts in patients with baseline platelet count > 150 x103/mm3 after vaccination or the unvaccinated patients. (table 1) The PT, fibrinogen and d-dimer in the vaccinated patients did not show significant differences, and aPTT was slightly decreased but in normal range, when we compared the figures of one week and three weeks following the vaccination. (Table 2) When the vaccinated patients were divided by baseline platelet count (more or less than 150 x103/mm3), there was no difference for coagulation factors between divided groups. Anti-PF4 antibody tests, which were performed three weeks after the vaccination, were negative in the all vaccinated patients. Conclusions: The vaccination with ChAdOx1 nCov-19 did not cause significant influence on platelet and coagulation factors in hemodialysis patients. The results for anti-PF4 antibody tests also did not show the risk and possibility of VITT. The vaccination for hemodialysis patients would be safe modality to prevent COVID-19 infection.