Abstract: A reaction device for a tiny organism includes a chamber, a first support plate, a second support plate and a separation plate. The tiny organism and a culture medium are added in the chamber. The first support plate is disposed on an opening of the chamber. The second support plate is disposed on one side opposite to the side on which the first support plate is disposed, and a third hole and a fourth hole separately correspond to a first hole and a second hole of the first support plate. A first end of the separation plate is located inside the chamber, the first end of the separation plate is spaced from the bottom of the chamber by a predetermined distance, a second end of the separation plate passes through the first support plate to connect to the second support plate.