RESUMEN En este trabajo se presenta una tecnica no invasiva de medida, para caracterizar dielectricamente emulsiones agua en aceite (w/o). Por primera vez se preparan en el laboratorio emulsiones w/o, con fases continuas de composicion quimica diferente: acido oleico y SAE40. Se emplea la tecnica de sonda coaxial que permite determinar en forma simultanea el porcentaje de agua de la emulsion y la influencia de la composicion de la fase continua en las propiedades dielectricas de la emulsion. Esto tiene un gran interes, pues emulsiones similares se pueden encontrar en varias industrias durante y al final de la produccion, tales como refinerias de petroleo, plantas quimicas, farmaceuticas etc. El conocimiento obtenido de las propiedades dielectricas permite predecir el comportamiento de las emulsiones ante la presencia de un campo electromagnetico, y posteriormente ser la base para el diseno de sensores para procesos industriales, o de laboratorio, donde se requiera separar y/o caracterizar emulsiones w/o. Palabras claves: Microondas, Sonda Coaxial, Emulsiones, Propiedades Dielectricas. ABSTRACT In this work, a non-invasive measurement technique is presented, to characterize the dielectric properties of Water in Oil emulsions (W/O). It is for the first time reported a comparison of w/o emulsions prepared with different continuous phases: oleic acid and mineral oil (SAE40). An open-ended coaxial probe is used to simultaneously determine the water percentage and the influence of the continuous phase chemical composition on the final emulsion dielectric properties. The results are of great interest because similar emulsions can be obtained in many industries during and after production processes, such us oil refineries, chemical plants, pharmaceutical plants, etc. The knowledge about the emulsions allows predicting their behaviour under the presence of an electromagnetic field, and can be used to design sensors or microwave applicators in industrial processes in which could be necessary to characterize or separate these W/O emulsions. Keywords: Microwaves, Open-ended Coaxial Probe, Emulsions, Dielectric Properties.