In our recent study of 2-flavor lattice QCD using chiral fermions, we find strong suppression of axial U(1) anomaly above the critical temperature of chiral phase transition. Our simulation data also indicate suppression of topological susceptibility compared to that predicted by the dilute instanton gas approximation (DIGA). In this talk, we present both of our theoretical and numerical evidence for disappearance of axial U(1) anomaly, emphasizing the importance of controlling lattice artifacts due to chiral symmetry violation, which is enhanced at high temperature.

Nonzero Temperature and Density