The aim of this study was to investigate the factors which affect HLA typing in 311 umbilical cord blood (UCB) samples. The HLA low resolution typing of UCB samples with misinterpreted HLA types from 311 UCB samples analyzed by PCR-SSO and PCR-SSP was performed. 7 samples difficult to determine their HLA genotype were sequenced directly and the reason leading to misinterpret HLA typing was analyzed. The results indicated that 99.4% of misinterpreted samples resulted from the restriction of HLA typing method itself and 0.6% of misinterpreted samples were suspected to be contaminated with maternal blood in UCB. It is concluded that HLA typing is mainly affected by the shortcomings of oligonucleotide probe design for PCR-SSO and lack of allele specific primers of PCR-SSP.