We recently proposed Li-rich vanadium monodiphosphate Li9V3(P2O7)3(PO4)2 as a novel polyanion-type cathode for rechargeable Li batteries. Herein, the Li9V3−x Al x (P2O7)3(PO4)2 solid solutions are obtained in different ratios of V and Al via solid-state reaction at 750°C in high-purity N2. The cell parameters (including a, c and V) of Li9V3−x Al x (P2O7)3(PO4)2 decrease in a linear way with Al-doping content. The intrinsic electronic conductivity of Al-doped samples reaches ∼10−7 Scm−1, which is more than one order of magnitude higher than that of the undoped one. The electrochemical insertion/extraction properties of the trigonal Li9V3−x Al x (P2O7)3(PO4)2 (x =0.00, 0.10, 0.25, and 0.50) phases are also presented. The Al-doped phases are demonstrated the better capacity retention and higher output voltage than that of the pristine one. After 30 cycles, Li9V2.75Al0.25(P2O7)3(PO4)2 can keep 92.4%, 87.7%, and 85.5% of the initial capacity under the current rates of 0.2C, 0.5C and 1.0C, respectively. The favorable voltage polarization, enhanced electronic conductivity, and dramatically contractible particle size after Al doping play significant contributions of comparatively good electrochemical performance of Li9V2.75Al0.25(P2O7)3(PO4)2 sample.