To investigate whether allelic polymorphism of haptoglobin (Hp) is associated with premature rupture of membrane (PROM), the Hp phenotypes of pregnant women with PROM were analyzed.The Hp phenotypes of 221 pregnant Korean women (187 control and 34 PROM patients) were determined by benzidine/hydrogen peroxide staining, following native polyacrylamide gel electrophoresis of hemoglobin-mixed sera. The Hp allele frequencies were calculated from the data of Hp phenotypes, and overall association with PROM was evaluated using Pearson Chi-Square test.The polymorphic distribution of the patients cohort who underwent a normal delivery (control group) was similar to that of healthy Koreans. In contrast, however, patients with PROM showed significantly higher occurrence of the Hp 1-1 phenotype than control group (23.5% vs 8.0%). Hp 2-2 phenotype was lower in PROM cohort (38.2%) than in the control group (48.7%). The Hp(1) allele frequency in PROM group was significantly higher than that in the control group (0.426 vs 0.297, p = 0.034) with odds ratio of 1.762 (95% CI: 1.038 - 2.991).These findings suggest that pregnant Korean women who possess Hp(1) allele (expressed as Hp 1-1 phenotype) have higher incidence of PROM than women with Hp(2) allele (expressed as Hp 2-2 phenotype). This is the first study that evaluated the significance of Hp polymorphism with respect to the development of PROM.