In this paper, the effects of annealing time on the dielectric properties of the Spark Plasma Sintered (SPS) BaMn₃Ti₄O_14.25 pellets were detail studied by the crystal structure analysis, micro structural observation and electrical properties research. The results showed that long annealing time was beneficial to the recovery of crystal structure damage caused by SPS, the formation of a reoxidation layer at the surface of grains and decreasing of the electrically insulating phase. All of these resulted in an increase in dielectric constant and loss, and a reduction in breakdown voltage.