This invention concerns a process for obtaining lactic acid in a single stage by direct oxidation in an aqueous medium of 1,2-propanediol in the presence of a mixture of heterogeneous catalysts, in conditions of low temperature and low pressure. The reaction takes place in the presence of oxygen and a mixture of heterogeneous catalysts, consisting of a first catalyst of noble metal supported in metallic oxide, and a second basic solid catalyst. The mixture of catalysts is easily recovered by filtration at the end of the process, to be reused. The lactic acid is obtained directly, with selectivity between 50% and 97%.