This paper presents a microwave sensor based on planar cross-shaped resonator (CSR), for the elemental solution measurements of wireless fungus sensing system. With the use of CSR and microstrip gap, the proposed sensor can offer additional dimensions of microwave insertion responses and differential characterizations for sensitive permittivity analysis of the solutions. The resonance properties are response of the solution with different concentrations to the sensing pads. To illustrate the technique, a prototype of the proposed sensor is fabricated and tested with two solution samples. It is found that the sensor designed at 3 GHz can detect the concentration change of sodium chloride from 0% to 6% with the sensitivity of 0.176 dB/(mmol/L), and ethanol from 0 to 95% with the sensitivity of 0.696 dB/(mol/L) and 0.023 GHz/(mol/L). This novel technique can lead to new insights for biomedical and biotechnological applications.