The objective of this study was to analyze the genotype distributions and allele frequencies for ROCK2 Thr431Asn and Arg83Lys polymorphisms among breast cancer patients. In this case control study, 223 patients with breast cancer were recruited and divided into two groups according to metastases (n = 128) and without metastases (n = 95). Genomic DNA from the patients and the control cases (n = 150) was analyzed by real-time PCR using a Light-Cycler. Neither genotype distributions nor the allele frequencies for the Arg83Lys polymorphism showed a significant difference between the groups. Although no marked changes were observed with nonmetastatic group, a statistically significant association was found between the control and metastatic group for the Thr431 Asn polymorphism. Although homozygous carriers of the Thr431Thr genotype were more frequent, heterozygous carriers of the Thr431Asn genotype were less frequent among the metastatic patients than among controls. There was also an increase in Thr431 allele (60.5% in patients vs. 51.7% in controls) and decrease in Asn431 allele frequencies (48.3% in control vs. 39.5% in metastatic patients) in metastatic groups (p = 0.036). Our results demonstrate that Thr431 Asn polymorphism of the ROCK2 gene could be a risk factor for the metastases of the breast cancer, and may help in predicting the prognosis.