(1) The major constituents of sea water from the Western Pacific Ocean near Japan have been quantitatively determined. The analytical results are as follows: the difference in the compositions between the world’s average and the Western Pacific is very small, except that the values of sodium and potassium are a little lower, while those of chloride and magnesium are but slightly higher, in the latter than in the former. (2) It is quite noteworthy that there is an astonishing agreement between the analytical results of the west and the northeast side of the Pacific Ocean. (3) A new indicator has been used for the determination of chlorinity; that is a mixed solution of fluorescein and starch. The superiority of this indicator has been briefly discussed. In conclusion, the author wishes to express his hearty thanks to Prof. T. Okada, Director of the Central Meteorological Observatory of Japan, for his kind guidance and the permission of publishing this report. He is also indebted to Mr. H. Matui for his earnest assistance throughout this work.