Background: Defects of manganese superoxide dismutase (MnSOD) have long been implicated in generation of oxidative stress and risk susceptibility to various cancers. Two functional polymorphisms within the MnSOD gene, including the Val-9Ala of the mitochondrial targeting sequence (MTS) and the Ile58Thr of the exon-3, have been proposed to reduce its enzyme activity and antioxidant potential. Materials and Methods: A high-throughput multiplex SNaPshot$^{(R)}$ system was developed herein for simultaneous analyses of Val-9Ala and Ile58Thr in a single reaction. Genomic DNA extracted from each whole blood sample of 248 patients including 107 with cervical cancer and 141 with breast cancer and from 136 healthy women as controls was analyzed by the multiplex SNaPshot$^{(R)}$ system. Results: The Val/Val, Val/Ala genotypes and the Val allele of the MTS were predominant in patients with cervical or breast cancer as well as healthy women in Thailand. The Ile/Ile genotype and the Ile allele of the exon-3 were found in all of them whereas none of the Ile/Thr, the Thr/Thr genotypes and the Thr allele was detected. Genotypic association of both Val-9Ala and Ile58Thr polymorphisms with cervical cancer and breast cancer of these patients comparing to healthy women was not statistically significant (p<0.05). Conclusions: The Val/Val, Val/Ala genotypes and the Val allele of the MTS were found predominantly but the Ile/Ile genotype and the Ile allele of the exon-3 were detected in patients with cervical cancer, breast cancer and healthy women in Thailand. These two functional polymorphisms (Val-9Ala and Ile58Thr) in MnSOD gene did not associate with susceptibility risk of these cancer patients in Thailand.