Geomagnetic measurements, using a proton precession magnetometer with a short sampling interval of approximately one second, were carried out to investigate a measurement error due to towing attitude of the sensor vehicle. The major results of the measurements are as follows. 1) An increase of towing speed of the sensor does not significant1y affect the magnitude of a measurement noise level, if an available stabilizer is attached to the sensor vehicle. 2) Towing the sensor with a drag rope of 15m long or without any stabilizer causes an increment of noise level in comparison with the case of towing with the available stabilizers. 3) Sea condition is clearly related with the measurement noise level. These results suggest that the error of the sea surface geomagnetic measurements is mainly related with a motion of the towed sensor vehicle.