New-generation low-emission transportation systems demand high-performance lithiumion (Li-ion) batteries with high safety insurance at broad operable temperatures. Highly conductive solid electrolyte is one of the key components for such applications. The objective of this thesis is to synthesize and characterize aluminum doped lithium titanium phosphate, i.e. Li1+xAlxTi2-x(PO4)3 (LATP), one of the solid-state electrolytes for potential applications to all solid-state lithium-ion batteries. In this research, sol-gel method and onestep solid-state reaction approaches were explored and critical processes were optimized towards maximizing lithium ion conductivities at room temperature. The impacts of the processing conditions on the structures, morphologies, compositions of the LATP products, and lithium ion conductions were presented. Particle growth kinetics and lithium ion conduction mechanism were briefly discussed. The highest conductivities of LATPs achieved via the sol-gel and solid-state synthesis are 1.24E-04 S/cm and 1.86E-04 S/cm, respectively, exhibiting the feasibilities of applying them to all-solid-state Li-ion batteries.