This paper reports a technique for quantification of beta-amyloid protein by the use of photo sensitive thin film transistor (p-TFT). In recent studies, a beta-amyloid protein has strongly related a central role of the pathogenesis of Alzheimer’s disease (AD) and AD-related olfactory sensory loss. In the p-TFT, we observed the difference of the photo-current according to the presence of the particles with beta-amyloid, RAW 264.7 cells, and olfactory receptor neuron cells. The p-TFT shows the drain current reduction of about 50μA is caused by the RAW 264.7 cells with magnetic beads and beta-amyloid. Therefore, we suggest a new method of detecting small quantity of A-beta for early diagnosis of AD by using photo-sensitive thin film transistor (p-TFT) devices.