Soft magnetic Mumetal thin film was fabricated under magnetic field at various substrate temperatures. High vacuum annealing was carried out at 200$^{C}$ during 1 hr. The in-plane anisotropy of Mumetal thin film was determined from hysteresis loops measured by VSM when the sample axis varied from the field direction from 0°to 180°. As the substrate temperature increases, the coercivity in easy direction decreases, but uniaxial anisotropy deviates from the field direction. After vacuum annealing at 200$^{C}$ for 1 hr, the uniaxial anisotropy is improved irrespective of substrate temperature. When the substrate temperature was 50$^{C}$, the anisotropy field is 4.3 Oe. As the substrate temperature increases anisotropy field decreases. Uniaxial anisotropy of Mumetal thin film was formed best at 50$^{C}$ before and after annealing.