Objective: Recently, it has been proven that interaction between the uterine natural killer-cells and fetal trophoblasts is a key factor in successful implantation. In human, the trophoblast cells express less Polymorphic, non- classical MHC and classical HLA-C that is highly polymorphic. Interaction between HLA-C molecule and the receptors on uNK Cells result in release of a variety cytokines and chemokines that modulate placental relationship between mother and her fetus. Therefore investigation of parental HLA-C and maternal KIR genes is interesting for determining the role of these genes in occurrence of recurrent miscarriage. Materials and Methods: We have screened the couples who have referred to Royan Institute for finding the cases of idiopathic abortion. We have done genotyping for maternal KIR/ parental HLA-C genes using the PCR-sequence-specific primer method and compare with control group who have normal pregnancy. Results: HLA-C molecules recognized by KIR can be divided into C1 and C2 phenotype that discriminated by different amino acids at position 80. Accordingly, all of the control group were heterogeneous (C1\C2) for this locus and genotyping of patients is ongoing that will be presented after performing of analysis and compare to controls. Conclusion: Whereas KIR /HLA-C genes intensively polymorphic, any of particular maternal KIR/parental HLA-C genotypes may have different effect on success of pregnancy. In order to access probable fetal HLA-C genotype, determination of parental HLA-C genotypes is required for identifying the role of any HLA-C allotypes or its specific receptors on the uNK- cell function related to miscarriage.