The present invention relates to a method for detecting the presence and/or the reaction of a biomolecule by monitoring changes of electrical property accurately according to the biological, biochemical or chemical reaction of the biomolecule, and a biochip provided for this purpose. The present invention provides a method for detecting the presence and/or the reaction of a biomolecule in a target sample, wherein the reaction of the target sample is performed under known reaction solution, in which a reference fluid having a high dielectric constant such as water is filled into a reaction chamber before the reaction to measure an impedance value or a capacitance value, after completing the reaction, the reaction solution is removed and said reference fluid having a high dielectric constant is refilled to measure an impedance value or a capacitance value, and then the impedance value or the capacitance value measured before and after the reaction is compared with each other.