This paper presents a simple and direct biomolecule detection scheme based on a coplanar waveguide (CPW)to-slotline ring resonator whose resonant frequency is 3.4 GHz. Its sensitivity enhancing technique and characterization is also reported. When a biomolecule is attached on the resonator, it directly detects the biomolecule through its resonant frequency change without any additional transduction procedures. The microwave biosensor is composed of a substrate and a metal resonator (nickel and gold). For higher sensitivity, the structure was modified by adopting an insulation layer between a nickel and a gold layer. Two types of the microwave biosensor were characterized through biotin-streptavidin reaction. Measurement results showed that resonant frequency decreased 65 MHz and 10 MHz for the original type, and 79MHz and 18 MHz for the modified type when biotin and streptavidin is attached, respectively.