The effect of Mo loadings and preparation methods, slurry and conventional impregnation, on the performances of alumina-supported MoO3 catalysts in transesterification of dimethyl oxalate (DMO) with phenol was investigated. Slurry prepared MoO3/gamma-Al2O3 catalyst exhibited higher activity and dispersion capacity than conventional one. Slurry MoO3/water was used instead of an ammonium heptamolybdate solution. Highly dispersed amorphous Mo catalysts were obtained, closely related to the catalytic activities without calcination, waste solutions, and calcining nitrogenous gases.