In recent years, the application of high magnetic field in material processing has received much attention from many researchers. However, most studies focus on single-phase solidification or eutectic solidification. The effect of high magnetic field on peritectic alloy is rarely reported. In this study, the solidification experiments on a Mn-56.5 wt%Sb peritectic alloy are carried out under high magnetic fields up to 11.5 T. According to the temperature curve recorded during solidification, it is revealed that high magnetic field increases the liquidus temperature and this rise increases with magnetic flux density increasing. The liquidus temperature rises by about 3 ℃ when the magnetic flux density is 11.5 T. On the contrary, no obvious change in peritectic temperature is found. In addition, the solidified microstructure is analyzed by quantitative metallographic analysis and the result shows that the amount of MnSb phase decreases markedly by the application of high magnetic field. This result consists with the change of phase transition temperature. By the X-ray diffraction, it is found that the c axis of MnSb crystal and (311) plane of Mn2Sb are perpendicular and parallel to the direction of high magnetic field,respectively. Furthermore, the solidification experiments with different cooling rates are also carried out. The quantitative metallographic analysis reveals that the effect of high magnetic field on solidified microstructure is affected by cooling rate. With the increase in cooling rate, the effect of high magnetic field on the fraction of MnSb phase fraction is weakened.