In order to examine distribution of atmospheric CO2 concentration over the central and western Pacific Ocean and elucidate factors governing the distribution, shipboard measurements were made between 1992 and 1996. Large variations in the concentration were observed in the northernmost and the tropical regions during the cruises. Also, year-to-year differences in the latitudinal CO2 distribution were detected. To interpret these variations, analyses were performed in terms of atmospheric transport from various source regions using meteorological and climatological data. The following results were obtained: (1) Episodic large CO2 variations appeared north of 30¿N over the central and western Pacific during the periods of ship cruises. These variations were related with exchanges of continental and marine air masses associated with movements of weather systems. (2) Discontinuous changes of CO2 concentration were observed in the equatorial region during spring cruises, reflecting suppression of interhemispheric air mixing. However, the magnitude, the sharpness, and the location of these discontinuous changes were associated with variations in the strength of air convergence and the movement of enhanced convective areas, and were quite variable. (3) Differences in the latitudinal CO2 gradient from northern low latitudes to southern low latitudes were found between each spring cruise. Comparison with climatological data suggests that the difference in the CO2 gradient is related to variation in the anomaly of meridional wind component distribution over the central and western Pacific at low latitudes.