In this paper, we report for the first time a one-pot reaction enabling total transformation of lactic acid to acetic acid over a Mo-V-Nb mixed oxide catalyst having an optimal atomic ratio 19:5:1. The mechanism of the reaction consists in two parallel ways leading to acetic acid: (i) oxi-dehydrogenation of lactic acid to pyruvic acid followed by decarboxylation and (ii) decarbonylation of lactic acid to acetaldehyde followed by oxidation. In the operating conditions we used, the catalyst is very active (total conversion of lactic acid) and selective towards acetic acid (100% selectivity). A 100% yield into acetic acid is hence obtained.