We investigated thermoelectric properties of higher manganese silicide obtained by the simultaneous use of ball milling and flash spark plasma sintering (FSPS) technique, and the results were compared those of the samples prepared with conventional spark plasma sintering (SPS). Despite the very short sintering process less than 50 s, FSPS samples reproduced well the crystallographic and thermoelectric properties of SPS sample made with long sintering time with more than 3500 s. Notably, the grain growth was significantly suppressed in the FSPS samples, although it has had minor effects on the transport properties.