In this paper, we are going to investigate insulin, a bio-molecule responsible for the onset of diabetes, which is generally diagnosed using the conventional ELISA method. Its picomolar concentration in blood and short life time was a challenge in developing a sensor sensitive to such small volumes. This paper presents an experimental study of the dielectric properties of hepes buffer solution with varying concentration of insulin, a peptide hormone at microwave frequency range. A composite whispering gallery electric mode (WGE(800)) microwave dielectric resonator with sapphire and polycarbonate disposable sample holding disc has been used at 17.59 GHz. From observations, imaginary part of permittivity has been found very sensitive to changes in insulin concentration ranging from 2.0327x10(-8)% to 21.9995x10(-8)%. Studies show that the present method has the potential to detect and sense ultralow concentration of bioanalyte with regression coefficient 0.943 and sensitivity of 0.039 for 10 pM change in insulin concentration.