A novel cost-effective flexible microwave sensor is proposed to facilitate point-of-care testing (POCT) methods for medical diagnosis. The sensor is based on the complementary split-ring resonator (CSRR) for accurate measurement of the permittivity of biomaterials. Using this method, the measurement of the permittivity over a wide range of frequencies can be achieved. This capability can be used to characterize various materials under tests (MUT) such as blood, saliva, tissue samples, etc.. The flexibility of the proposed sensor makes it possible to use it when the accessibility of the sample has technical difficulties such as curved surfaces. Firstly, the optimized structure as well as coupling to the readout transmission line are evaluated using finite element method (FEM) simulations. Then, the prototype of the optimized structure is fabricated on thin polydimethylsiloxane (PDMS) substrate which is a biocompatible and economical polymer. Based on the simulation and experimental results, a suitable conductive material for the fabrication of CSRR and readout parts is carefully chosen. The proposed flexible sensor is tested within in-vitro setups by recording the corresponding resonant frequency and quality factor for different materials. A high correlation between the scattering parameters of the proposed sensor and the variations in materials’ characteristics which principally occurs due to the difference in their dielectric properties, is attained. Our preliminary studies have shown that such a device is capable of using in clinically acceptable zones.