Relating the cost of the tidal power generation, the bio-fouling effects on the tidal turbine may be important since it is relevant to the maintenance cost of the power device for a long time. Field measurement results of the bio-fouling effects on test plates at the Hirado-Seto Strait in Nagasaki Prefecture are reported. Test plates include 5 plates without paint and a plate with silicon paint and 4 plates with anti-fouling offshore structure and ship bottom paints. The experimental frame with the test plates are hung from the breakwater into the sea and are raised from the sea every month regularly to observe the bio-fouling by taking pictures and measuring the weight of the plates. It is clarified that the dominant species around the adjacent sea are the triangle- and red-barnacles which do not newly attach if seawater temperature becomes below 20 degree in centigrade, but it continues to grow even in winter if it once attached. Observation is still running since September 2013 and the results for more than 3 years are presented.