Hydrogen peroxide (H2O2) is a reactive oxygen species that affects cell signaling in various plant defense responses and induces programmed cell death. To identify the new components associated with H2O2 signaling and tolerance, we conducted a genome-wide association study (GWAS) on the root growth of 133 Arabidopsis thaliana accessions grown in the presence of toxic H2O2 levels. The most significant SNPs were associated with a cluster of chromosome 4 genes encoding an aquaporin NODULIN 26-LIKE INTRINSIC PROTEIN 1; 1 (NIP1;1), an NB-ARC domain-containing disease resistance protein (AT4G19050), and a putative membrane lipoprotein (AT4G19070). The expression level of NIP1;1 was relatively high in A. thaliana accessions sensitive to H2O2. Additionally, overexpression of NIP1;1 in a tolerant accession (e.g., Col-0) increased the sensitivity of transgenic plants to H2O2. An in planta β-glucuronidase reporter assay revealed that variations in the NIP1;1 promoter were responsible for the differences of its expression level in H2O2-tolerant and -sensitive accessions. Cell death was extensive and H2O2 levels were high in the roots of H2O2-sensitive and NIP1;1-overexpressing accessions. Together, our results indicate that the aquaporin NIP1;1 is a key determinant of the sensitivity of A. thaliana to H2O2, and contributes to the phenotypic variations detected by our GWAS. © 2017 The Author