Crystalline porous Mo-V-Bi oxides (MoVBiO) were prepared by hydrothermal synthesis approach. The effects of organic additives (methanol and tartaric acid) on the morphology and particle size of the MoVBiO crystals were investigated. The size of MoVBiO crystals was tuned in the range of 30300 nm. It was found that the methanol accelerated the formation of crystal nuclei resulting in the crystallization of small particles (30 nm), while the tartaric acid inhibited the nucleation thus resulting in MoVBiO crystals with a size of 300 nm. The as-synthesized MoVBiO samples were used in the indirect oxidation of methanol to methyl formate. The MoVBiO crystals with a size of 30 nm synthesized with methanol, showed a high methyl nitrite conversion of 92 % and methyl formate selectivity of 94 % at 140 C. The catalyst exhibited a relatively slow but almost constant deactivation over 50 h due to the deposit of reaction species. The small MoVBiO crystals (30 nm) with more surface active sites and accessibility showed high performance in the oxidation of methanol to methyl formate in contrast to the big crystals (300 nm).