The microfabrication and testing of a Giant Magnetoresistance based microfluidic sensor for biomedical applications is presented in this work. Different processes involved during the fabrication of the GMR sensor such as electrodeposition, photolithography, etching, PDMS replication and glass bonding are clearly demonstrated in this book. The GMR based microfluidic sensor is able to detect the flow of ferrofluid, polystyrene superparamagnetic particles, dynabeads sheep anti-rabbit IgG and alexa fluor donkey anti-sheep bound to dynabeads sheep anti-rabbit IgG. The GMR device is able to produce varied output signals based on the flow rates and concentrations of different magnetic fluids pumped through its microchannel. Different output responses are observed with fluctuating input voltages of the GMR device. The GMR based microfluidic sensor is fabricated to be utilised in various biomedical applications and the obtained results are analyzed in this book.