We calculate the electronic structure of ambient liquid water (ALW) at 298 K under a pressure of 0.1 MPa using first principle molecular dynamics based on density functional theory. The effect of hydrogen bond (H-bond) on the electronic structure is focused by comparing partial densities of states of low-density amorphous ice (LDA) at 77 K and ALW. The results show that the H-bond number in LDA is larger than that in ALW. More complex H-bond networks of ALW than that of LDA have also been found by classical molecular dynamics calculations. (c) 2007 Elsevier B.V. All rights reserved.