Magnetization at 0.3 and 140 Hz (0-10 Oe) and magnetic relaxation measurements were carried out in detail in the temperature range between 4.2 and 300 K for a polycrystalline Fe65Ni35 alloy. The typical temperature Tg and the magnetic field Hg which correspond to the anomalous temperature in χ-T curves and inflection field in σ-H curves, respectively, are summarized and a H-T diagram is obtained. A strong magnetic relaxation is observed along the Hg-T line. The temperature dependence of Hg is discussed by the thermal activation of 180° domain wall which is pinned strongly by the antiferromagnetic-like clusters below Tg. It is find that H 1 2g is a linear function of T 2 3.