In this work, the Mn and Bi mixture prepared with and without compression were sintered in a vacuum at 325°C and cooled down naturally to obtain low-temperature phase MnBi. For non-compressed samples, the MnBi content increases with sintering time which could be described by the diffusion process. The average maximum energy product ((BH)max) values were 3.67, 3.05, and 4.77 MGOe for MnBi sintered for 24, 48, and 96 hr, respectively, consistent with their phase identifications. For the compressed samples, the MnBi phase is significantly low in the 24-hr sintered samples compared to the samples sintered for 48 and 96 hr. This resulted in an average (BH)max of 0.43, 3.90, and 3.23 MGOe for the compressed samples sintered for 24, 48 and 96 hr, respectively. The results suggest that compression of the Mn and Bi mixture affects the flow of liquid Bi during sintering and, thus, hinders the formation of MnBi. The effects of the compression were reduced for the prolonged sintered samples, suggesting changes in the internal structure as the sintering proceeded.