Navigation by Loran‐C was evaluated in comparison with GPS's data during theJean Charcotcruise for the French‐Japanese cooperative project, Kaiko. Simple overlapping mean of Loran‐C positions for five minutes showed a good relative accuracy of about 50 meters. Loran‐C positions, however, showed systematic shift up to one kilometer due to propagation delay of Loran‐C wave through land area. The value of the shift was measured in the south off the Japanese Islands; it was found that the shift of Loran‐C position can be corrected within an accuracy of about 100 meters in most cases by use of the correction table prepared by the Hydrographic Department of Japan. In a special case as the Loran‐C wave propagates over a high mountain area or along a long coastal line, the recommended correction procedure for propagation delay should be improved to correct the local effects (∼200m).