Summary Background & aims Recent studies have indicated a close relationship between hypertension and inflammation. Antioxidant substances, including β-carotene, are known to be preventive factors for hypertension. We investigated the effect of serum β-carotene levels on the association between the interleukin-1beta (IL-1B) C-31T polymorphism and hypertension. Methods Subjects were 625 inhabitants (200 males and 425 females) of Japan, aged 39–70 years, who attended a health check-up examination in 2003. The IL-1B C-31T polymorphism was genotyped by polymerase chain reaction with confronting two-pair primers. Serum β-carotene levels were measured using high-performance liquid chromatography. Results The TT genotype of IL-1B C-31T was associated with an increased risk of hypertension in all subjects (Odds Ratio [OR] = 1.82, 95% Confidence Interval [95% CI] = 1.09–3.06, compared with CC genotype). Among male CC carriers, those with high serum β-carotene levels had a significantly lower OR (OR = 0.25, 95% CI = 0.06–0.95) for hypertension relative to those with low serum β-carotene levels. The TT carriers had a significantly higher OR compared with the CC carriers among males with high serum β-carotene levels (OR = 5.03, 95% CI = 1.34–21.58) and among females with low serum β-carotene levels (OR = 2.47, 95% CI = 1.04–6.00). Conclusion This study suggests that the IL-1B C-31T polymorphism is associated with hypertension, and that this association is modulated by serum β-carotene levels.