The relation between the microstructure and the magnetic properties of Fe₂P-type (Mn,Fe)₂(P,Si,B) based materials has been systematically investigated by changing the annealing temperature and time. X-ray diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy measurements show that the alloys contain the main Fe₂P-type phase and two impurity phases of (Fe,Mn)₅Si₃-type and Fe₂MnSi-type. Boron appears to facilitate the formation of the Fe₂P-type phase during the arc-melting progress. Upon increasing the annealing temperatures from 1123 to 1423 K, the Curie temperature (T_C) decreases from 302.0 to 270.5 K in the Mn_1.15Fe_0.85P_0.55Si_0.45 alloys and the magnetic-entropy change (ΔS_M) increases linearly with annealing temperature. For the Mn_1.15Fe_0.85P_0.52Si_0.45B_0.03 alloys annealed at 1423 K for different times, T_C decreases from 263.8 and 232.8 K with increasing annealing time and ΔS_M reaches a maximum value after annealing for 48 h. The differences in the annealing temperature and time influence the Si content in the Fe₂P-type phase of the alloys and determine T_C, the thermal hysteresis and the magneto-elastic transition.