Provided is an apparatus for detecting bio materials and a method for detecting bio materials by using the apparatus. The apparatus includes a bio material reacting unit, an optical source unit, and a detecting unit. The bio material reacting unit includes bio sensing materials immobilized on gold nanoparticles. The optical source unit emits light toward the bio material reacting unit. The detecting unit measures variations of surface absorbance of the gold nanoparticles by detecting light transmitted through the bio material reacting unit before and after a bio material is bound to the bio sensing materials.