The frequency of Rhesus D negative blood group in Omanis is 8.35% but the molecular background of this phenotype is unknown in the Omani population. The Rhesus D negative phenotype has a high molecular diversity. We report a rare case of serological D negative with existence of complete RHD gene in a 43-year-old Omani male blood donor. Molecular analysis of RHD exons showed duplication across the boundary of intron 3 and exon 4. This is a 37 bp insert in RHD exon 4 along with c.609 G>A mutation. We are uncertain if the presence of RHDΨ is homozygous (RHDΨ/RHDΨ) or hemizygous (RHDΨ/del). Therefore, molecular basis of D zygosity determination would be a good approach to further explore the case.