For the spatial and temporal observations of surface pCO₂ in the ocean, we have been developing a compact drifting buoy system equipped with pCO₂ sensor. In general, when the buoy system is utilized for a long-term in situ observation, the instruments are susceptible to biofouling in the form of microbial and algal films. The biofouling affects the operation, maintenance and data quality of the deployed instruments. Tributyltin was the most effective biocide used in modern antifouling paints, but affected adversely the marine environment. To ascertain whether biocide free, silicon-based antifouling paint can be used for the oceanic platforms and instruments, the antifouling tests of silicon-based paints were carried out with other types of paints. After 500 days, one of silicon-based paints showed the lowest fouling coverage (25%) on the painting surface among the antifouling paints tested, indicating the high effectiveness as regards the prevention of marine biofouling. Hence, the silicon-based antifouling paint was used as biofouling prevention for our drifting buoy system.