We proposed a highly sensitive twin-core Photonic Crystal Fiber (PCF) biosensor based on Surface Plasmon Resonance (SPR). This biosensor consists of a dual-core that is formed with small circular air holes and a circular-shaped cladding made up of large air holes. Silica was selected as the background material. The gold is used as a plasmonic material to enhance the electric field inside the sensor due to it has negative permittivity. We chose the gold layer width to be 30 and 35 nm. The numerical analysis was performed using COMSOL Multiphysics v5.5.With distinct refractive indices (RI) of (WBC = 1.36), (Hemoglobin = 1.38), and (RBC = 1.40), this proposed model has a high resolution, a peak amplitude sensitivity (AS), and the highest wavelength sensitivity(WS) of 1x10(-3) RIU, 943.813 RIU-1, and 10000 nm/RIU, respectively. Besides, this biosensor expresses the relative sensitivity of 95.3%, 95.03%, and 97.66% for WBC, HB, and RBC, respectively.