This paper presents a microwave sensor composed of one millifluidic channel that operates over a frequency range from 1 GHz to 4 GHz and is used for microwave spectroscopy of liquids with millilitre volumes. The accuracy of the device is first evaluated with BSA solutions of different concentrations and then with complex biological liquids such as hen egg yolk and albumen samples. Low standard deviations of the measured values of modulus and phase contrasts of the transmission coefficient S21 are obtained. These values correspond to 0.02 and 0,18 respectively for BSA solutions, as well as 0.05 and 0.03 for 10 samples of hen egg yolk and white respectively over the selected frequency range. Such accuracies enable the use of such a sensor for various applicative domains, including agronomy for which the investigation of the dielectric properties of eggs may be of interest for quality, freshness or status discrimination purpose.