Highly dense n-type Bi 2 Te 3 -based thermoelectric materials dispersed with xvol.% γ-Al 2 O 3 nanoparticles (x=0, 0.4, 1.0, 1.5) were fabricated by spark plasma sintering method. The effects of γ-Al 2 O 3 addition on microstructure and the thermoelectric properties were studied. It was found that γ-Al 2 O 3 nanoparticles locate both at grain boundaries and inside Bi 2 Se 0.3 Te 2.7 grains. The nanoparticles induce both potential barrier scattering effect and additional phonon scattering effect, which simultaneously enhance the Seebeck coefficient and reduce the lattice thermal conductivity of the nanocomposites in the measured temperature range of 300–500K, respectively. The maximum dimensionless figure of merit (ZT max ) reaches up to 0.99 for the sample with x=1.0 at 400K, which is 35% improvement over the Bi 2 Te 3 -based matrix. More importantly, the average ZT value of the sample increases from 0.65 to 0.91 in the temperature range 300–500K, making the nanocomposites much more applicable in cooling and power generation.