Mg2-xZnxSi0.99Sb0.01(0 ≤ x ≤ 0.1) solid solutions were prepared by B2O3 flux method combined with spark plasma sintering (SPS) technique. The electrical conductivity, Seebeck coefficient and thermal conductivity have been measured as a function of temperature from 300 K to 780 K. The lattice thermal conductivity reduces upon Zn substitution, however, the electrical conductivity first decreases and then increases with Zn content increasing. The underlying mechanism was discussed. Among the samples, the maximum PF of 1.76 mWm-1K-2 at x=0.075 was obtained at 780 K, about 18% higher than that of Mg2Si0.99Sb0.01.The lowest lattice thermal conductivity of 2.86 Wm-1K-1 is obtained at 770 K for the x=0.1 sample. As a result, a maximum dimensionless figure of merit of 0.37 was obtained for Mg1.9Zn0.1Si0.99Sb0.01 at 780 K .