This paper has the aim to explain the machanism of oxoesterification of methanol over Mo -Sn -Ox oxide catalyst in the gas phase. Previous studies of similar oxide systems have already proposed a few mechanisms of this reaction. The acid-base, redox properties and catalytic activity in oxoesterification of methanol in the gas phase were investigated for Mo -Sn -Ox oxide catalyst with various Mo/Sn compositions. Reducibility of Mo and Sn species in Mo -Sn -Ox catalyst was studied by temperature-programmed reduction (TPR) in H2 atmosphere. The acidity of this catalyst was studied by means of pyridine absorption and infrared spectroscopic techniques (FTIR). The temperature dependence of conversion of methanol to methylformate was investigated in the integral flow reactor. The character of surface species resulting from methanol, formaldehyde and methyl formate absorption was studied by FTIR spectroscopy.