Nuclear and civil engineering structures are subjected to environmental conditions (rain, wind, temperature variations, etc.), as well as to various physical, mechanical and chemical aggressions that affect their durability. There are two types of methods for assessing structures durability: destructive methods (D) and non-destructive methods (ND). ND techniques are preferred in areas where there are limits on direct destructive methods such as the difficulty of extracting samples (accessibility, sensitivity of the structure). Monitoring approaches are complementary to ND investigation because they allow continuous recording even in inaccessible areas with limitation of human intervention. In our work, we are interested in the development of an embedded capacitive sensor. Thus, in this paper, we propose the use of standard liquids (with well-known permittivity values) in order to carry out a prior calibration of the sensor which will be embedded later in reinforced concrete structures. Liquids were selected for their relative permittivities that cover the concrete range (2 to 30) at the frequency range of capacitive method. Liquid permittivities are extracted on one hand from literature review. On the other hand, measurements were performed with two coaxial probes. These probes were developed in research works and their principle consists on an open-ended coaxial line connected to a network analyzer. The obtained dispersion curves of the permittivities were adjusted then with the Debye model. Results show that Debye's model can adjust our measurements with a good correlation. Permittivity values in the working frequency range of the capacitive probe are thus extracted and compared to values published in literature. Once calibration is done, capacitive sensor is ready to be embedded in concrete to monitor reinforced concrete nuclear structures.