The iron losses and acoustic noises of a model transformer core made of grain-oriented electrical steel sheets were investigated under DC biased magnetization while altering the amplitude of magnetic flux density, B_m, and the DC biased magnetic field, H_DC, applied by the third windings. The iron loss increased as H_DC increased up to100 A/m, while over 100 A/m, the increment of iron loss by DC biased field rapidly decreased. The increase in iron loss at the same H_DC was largest at B_m:1.1−1.5 T. Meanwhile, the acoustic noise increased monotonically as H_DC increased. The acoustic noise of odd-order harmonics was drastically increased under DC biased magnetization, and this is the primary cause of the increase in acoustic noise.