Glutathione S-transferase P1 (GSTP1) is involved in a wide range of detoxifying reactions. Any alteration in the structure, function, or expression of GSTP1 gene may alter the ability of a cell to inactivate carcinogens or mutagens, and thus modify an individual's risk to cancer. Previous epidemiological studies on the potential association between GSTP1 Ile105Val polymorphism and breast cancer risk have produced inconsistent results. In order to drive a more precise estimation of this association, we performed a meta-analysis of 30 published case-control studies including 15,901 cases and 18,757 controls. Crude odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of the association. The results of this meta-analysis showed that GSTP1 Ile105Val polymorphism was not associated with breast cancer susceptibility in overall population. However, in subgroup analysis by ethnicity, we found a significant association among Asian population (for Val/Val vs. Ile/Ile: OR 1.27, 95% CI 1.02-1.83; for the recessive model Val/Val vs. Ile/Ile + Ile/Val: OR 1.42, 95% CI 1.20-1.69). When stratified by study design, significantly elevated susceptibility to breast cancer was found among hospital-based studies (for Val/Val vs. Ile/Ile: OR 1.38, 95% CI 1.16-1.63; for recessive model Val/Val vs. Ile/Val + Ile/Ile: OR 1.31, 95% CI 1.12-1.55; for dominant model: Val/Val + Ile/Val vs. Ile/Ile: OR 1.10, 95% CI 1.02-1.19). In conclusion, our meta-analysis suggests that GSTP1 Ile105Val polymorphism may increase susceptibility to breast cancer in Asian population.