Introduction: One of the goals of modern genetics is to develope safe prenatal diagnostic tests which do not constitute any risk to the fetus. One potentially non-invasive approach for doing so is to obtain fetal material from the maternal circulation. In this study we obtained Rlaternal blood from the pregnant women and tried to determine sex of fetus by nested-PCR. Material and Methods: To determine the sensitivity of the PCR methods, artificial samples were prepared first by mixing whole blood of adult males with that of the adult females. After performing DNA extraction, PCR was optimized on these samples. Whole blood samples were then obtained from 70 pregnant women in 8 to 12 weeks of gestation after considering the medical ethics. In this study we tried to extract the DNA of the white blood cells (WBC) as well as free DNA of serum and plasma of the maternal bloods and performed Nested-PCR using primers flanking the specific-sequence of V-chromosome or Sex determining region on Y (SRY). If the fetus was male, the size of amplified fragment of the first round product was about 470 base pairs and second round was 254 base pairs. Results: After delivery, Only 32 out of 70 of the samples could be followed and results showed that 18 were male. However, the results of the nested-PCR examination of the serums indicated that 21 of the fetas were male and examination of the WBCs showed that 22 were male, in each group 3 and 4 cases were misinterpreted respectively. So the accuracy of sex determination of the samples in serums and WBCs were 90.62 % and 81.25% respectively which is almost similar to the recent reports (91.5%). We could not obtain good results from the free DNA of the plasma. Conclusion: We have obtained relatively positive results from the analysis of maternal blood and if we could follow all cases to see the results of all deliveries, we could then reconfirm the results of our research. Anyway we hope this project could be able to introduce this new approach as means of noninvasive prenatal diagnosis for detection of common inherited diseases in Iran.