Microbial screening tests of umbilical cord blood (UCB) are essential for stem cell transplantation. We analyzed the microbial contamination rate and distribution of isolated microorganisms over 10 years of samples from the MEDIPOST Cord Blood Bank. In addition, we studied the influence of inoculum volume microorganism culture and compared the yield and speed of microorganism detection. Methods: Microbial screening tests were performed using a manual method, which includes using an inoculum of 2 mL of plasma, a byproduct of UCB processing from pediatric culture bottles. When positive blood culture was detected, each set was once again inoculated with 2 mL and 4 mL of plasma. Results: From 2004 to 2013, a total of 133,610 UCB units were screened, of which 1,311 (0.9%) tested positive for contamination. The most frequently identified microorganism was Escherichia coli (34.6%), followed by Bacillus spp. (12.8%), Enterococcus faecalis (5.3%) and Klebsiella pneumoniae (4.4%). The total yield rate increased by 0.2% over this time period, although the yield rate of Bacillus spp. increased by 8.3%. Conclusion: The results of this study could be used in many ways with both domestic and international data regarding cord blood contamination. Also, other microbiology laboratories using culture conditions similar to ours could refer this study when preparing guidelines. Finally, by detecting low levels of bacteria, we have contributed to cord blood safety. (Ann Clin Microbiol 2016;19:1–6)