Background: This study aimed to determine the frequency of rare blood group antigens among pregnant women in Port Harcourt Metropolis. Methods:The frequencies of Rh antigens and phenotypes of the pregnant women in Port Harcourt Metropolis, Nigeria, were determined, using standard serologic techniques.Results: Of the 374 pregnant women studied, the frequencies of the Rh antigens within the population were D (89.0%), c (82.0%), e (54.0%), C (24.3%), E (20.1%). The frequencies of the Rh antithetical antigens were DD/Dd (91.2 %), Cc (19,5%), cc (84.5%), Ee (13.9%), ee (54.3%), CC (25.1%), EE (19.8%) and dd (10.4%). Seven (1.9%) were found to be Rh null , sixteen(4.3%) were found to be D--or exalted D. Phenotypes without RhD reactivity were -c-(2.9%), -Cc (0.3%), -C-(0.3%), -Ee (0.5%) and -E-(0.3%). The most frequently occurring Rh phenotype was Dccee with a frequency of (25.8%). RhD-ve was found to be significantly associated with HDN outcome ( 2=6.605 and P=0.01). Conclusion:We concluded that: 1) There is the presence of uncommon Rh phenotypes in our population. 2) Rh null exists in this study population of which similar studies have not been reported in Nigeria. 3) There is need to conduct studies in other parts of Nigeria in order to compare the frequencies of these rare blood groups in Nigerian population. 4) Molecular studies to establish reasons for deletion and Rh null phenotypes among Nigerian and Africans in general are hereby advocated.