Witches' broom disease which affects cacao tree (Theobroma cacao L.) is caused by the hemibiotrophic fungus Moniliophthora perniciosa. Studies of the cacao-M. perniciosa interaction showed that the pathogenicity of M. perniciosa is associated to the presence of oxalic acid (OA). In some organisms, OA can be degraded into formate and CO2 by the oxalate decarboxylase (OXDC) enzyme. Here, we used the oxdc gene from Flammulina velutipes to generate transgenic tomato plants as a potential strategy to control M. perniciosa infection. Three transgenic T1 lines expressing the oxdc gene were obtained and two of them (P4 and P16) presented a significant delay in symptom development and higher survival percentage when inoculated with M. perniciosa in comparison to the non-transformed wild-type (WT) plants. Moreover, the P16 line test showed a decreased production of H2O2 in the presence of OA in comparison to the WT, as evidenced by the 3,3'-diaminobenzidine test. These results indicate that the P16 transgenic line is able to break down OA leading to normal plant development with few symptoms even when infected by M. perniciosa. Phenotypic and histological analysis showed differences between WT and transgenic plants. The amount of fungus hyphae was lower with thinner thickness in the transgenic plants. This study evidences of the reduction of witches' broom disease progression by the presence of the oxdc gene leading to the plant survival.