Dissolved Oxygen sensor is used mainly in aquaculture industries and environmental sectors to measure the concentration of oxygen dissolved in water. The level of dissolved oxygen in water strongly affects the growth of organisms in aquaculture. There are many methods to measure the concentration of dissolved oxygen in water including colorimetric, titrimetric, and polarographic. Newly-developed technique uses optical principle to measure the reaction of oxygen to the fluorescent dye and the concentration of oxygen is calculated based on the Stern-Volmer equation. This work develops a very simple optical sensor based on this principle but uses extremely low-cost, off-the-shelf optical components for detection. The heart of the sensor is the AS7262 6-Channel Visible Spectral ID Device made by AMS. The sensor was built and tested against the commercial devices made by Extech (Model 407510). Preliminary results show a promising device which is very low cost, simple, low maintenance, and easy to use in the field to support aquaculture industries and environmental agencies.