CMOS image monitoring system for optimal measuring the activity of biosensor is developed using genetic algorithm. Most of living organism in water as water flea, fish, etc are frequently used as biological sensor for monitoring the water quality. It is very difficult to measure the activity of biosensor by image sensor because the value of measurement is varied with gathering method of biosensor images. The suggested monitoring system can optimally measures the activity of biosensor by genetic algorithm. The system is implemented with FPGA into the small hardware which is excellent in terms of the price and performance.