Natural gas is an abundant natural resource, consisting of mainly light alkanes. The utilization of these alkanes by selective oxidation has been widely investigated, and selective oxidation of propane has been one of the recent challenges. Among the most promising catalysts for this reaction are Mo-V-Te-Nb mixed metal oxides. The preparation method and the calcination procedure seem to be crucial to achieve high catalytic performance. In this work we prepared Mo-V-Te-Nb mixed oxides using hydrothermal synthesis. The phase composition of the crystalline product was controlled by varying the metal stochiometry and the thermal activation procedure. In this way, a series of single-, bi-, and multi-phase materials has been prepared. Samples were characterized before and after thermal activation using XRD, SEM-EDX, TEM, and BET measurements. The materials have been tested in the selective oxidation of propane to acrylic acid. The hydrothermal synthesis of Mo-Te-V-Nb mixed oxide results in amorphous materials with differing chemical homogeneity as revealed by SEM-EDX. During heat treatment, crystallization occurs. XRD and HRTEM indicate the formation of orthorhombic phases, referred to in the literature as M1 and M2, respectively.Other phases observed are M5O14 (M=Mo, V, Nb) and V0.95Mo0.97O5. Phase composition and homogeneity of the heat treated product is related to the composition of the precursor material. The specific elemental composition of the M1 phase is already reflected in fairly homogeneous precursors of single-phase M1 materials, which show improved catalytic performance compared to multi-phase materials prepared by hydrothermal synthesis.