The reaction between aromatic and aliphatic aldehydes and ketones with methoxylamine is promoted by cerium chloride. The antifungal activity of some methoxime derivatives against five postharvest phytopathogenic fungi, was examined, employing imazalil and carbendazim as positive controls, and the preliminary results are discussed. The target fungi were Rhizopus stolonifer, Botrytis cinerea, Penicillium digitatum, Penicillium italicum and Monilinia fructicola. These phytopathogens affect fruits worldwide, causing relevant economic damage. In all cases, minimum inhibitory concentrations and minimum fungicidal concentrations were obtained. Despite most of the simple compounds resulted inactive, preliminary results suggest that certain compounds display a structure-dependent activity which correlates with the length of the substituent attached to the oxime sp² carbon.