Three component data along the Magsat paths in the area of 110¿E-170¿E and 8¿N-68¿N were fitted by polynomial series of the coordinates of the satellite position along the path. The coefficients decrease sharply up to the sixth degre and become almost constant. The fields represented by the sixth degree polynomials were subtracted from the data to remove the core and the external fields. For the altitude correction a rectangular harmonic analysis was applied to the residuals thus obtained by employing local Cartesian coordinates. The residual fields were expanded into double Fourier series of the maximum order of n=m=3 over areas of 4000¿4000 km and 2000¿2000 km, and anomaly fields were computed for the satellite altitude. It was revealed that (1) an intense positive anomaly of the vertical component ran along the Kuril trench, (2) the Japan Sea was covered with a negative vertical anomaly in the northeastern part, and with a positive in the southwestern part, (3) there was a pair of positive and negative vertical anomalies covering the area from northern Korea to the East China Sea, suggesting the existence of an extremely localized magnetization like a dipole near the surface in the southwestern tip of the Korean Peninsula.