To reduce areas lacking data of surface seawater pCO2, which is an indispensable property for the evaluation of atmospheric CO2 uptake by the ocean, in 2016 we started a 5-year project to deploy drifting buoys with pCO2 sensors in the South Pacific. The drifting buoy is compact (diameter, 315 mm; height, 566 mm; weight, ~10 kg) and easy to manage. For efficient deployment, we determined appropriate deployment positions along a ship track by particle tracking experiments. During the MR16-09 cruise of R/V Mirai, we deployed seven drifting buoys. The tracks of drifting buoys generally followed those predicted by the experiments. pCO2 values observed by drifting buoys and considered to be reliable were on the whole within values expected from interpolated pCO2 values. However, the pCO2 sensor needs to be improved to raise the pCO2 observation yield ratio of each drifting buoy.