Mn55Bi45 melt - spun ribbons were prepared by using the melt-spinning technique followed by annealing in Ar/5%H2 gas mixture. The in-situ formation of ferromagnetic phase (denoted as LTP) of MnBi was observed by the multi-section cycled Differential Scanning Calorimetry (DSC) method. It was found that, the optimal annealing temperature range for forming MnBi LTP is 250 – 280 oC. The prolonging annealing time increases the content of MnBi LTP leading to the increase of saturation magnetization Ms but paid by the drop of the intrinsic coercivity iHc. The MnBi green powders were prepared by the Low Energy Ball Milling method (LEBM) in N2 liquid. The maximum energy product of MnBi green powders is estimated about 10.8 MGOe.