This paper presents an innovative high-frequency- based biosensor, which combines both microwave detection and microfluidic network for time-efficient and accurate biological analysis. It is composed of a coplanar waveguide with a microfluidic channel placed on top. With the help of an appropriate de-embedding technique and modeling of the measurements, the relative effective permittivity of human umbilical vein endothelial cells has been evaluated successfully. Furthermore, experiments have been performed with the sensor on various cell concentrations in suspension, which validates its use in bioengineering applications such as cell quantification and counting in solution. This sensor requires no direct contact or use of labels on the cells, contrary to other usual types of biosensors (optical, mechanical or dc/low-frequency-detection-based ones).