1) In order to make clear the fecundity and spawning of a puffer, Fugu rubripes T. et S., investigations were carried out in the central waters of the Inland Sea of Japan in April-May, I960-I961.
2) Distribution of the fishing grounds of Fugu rubripes in Bisan Strait was shown.
3) Morphological characteristics of the spawners of Fugu rubripes were clarified. Sex-ratio (female: male) of the spawners caught by seine-nets was approximately 1: 3. Females were significantly greater in weight than in males, while the difference in total length between both sexes was not significant.
4) Development of ovarian eggs seems to be advanced uniformly within an ovary, which makes reasonable to consider that the spawning may occur at a time or at least in a very short period.
5) Relationships of fecundity with total length and weight of body were clarified.
6) Successful collection of the eggs deposited on natural spawning beds was made. The data obtained in the present investigation show that the spawning beds of Fugu rubripes lie in the bottoms having particle-size of sand 2-4 mm. in diameter.