The interactions among nano-sized giant magnetoresistances (GMRs) which can affect the biosensor operation, were studied using micromagnetic simulations and micromagnetic analysis. The magnetic field energy, the magnetization distribution and the effective magnetic field were simulated for variable spacer distances, aspect ratios and external magnetic fields to study the interactions among the GMR sensors. And the spacer distance should be at least 1000 nm to eliminate interference between 1000 nm×100 nm×9 nm or larger GMRs in an array, while the aspect ratio should be more than 10 to improve the sensor sensitivity and stability. Micromagnetic energy theory is used to explain the simulation results.