We studied oocyte steroidogenesis in relation to oocyte development in the greenling, Hexagrammos otakii, a marine multiple spawner. Vitellogenic and mature oocytes were incubated in vitro in the presence or absence of $[^3H]-17;{alpha}-hydroxyprogesterone$ as a precursor. The major metabolites were androgens [androstenedione $(A)_4)$ and testosterone (T)] and estrogens [$17;{eta}-estradiol;(E_2)$ and estrone ($E_1$)] in vitellogenic oocytes. The metabolic rate of T was lower in 1.08 to 12-mm oocytes, while that of $E_2$ increased with oocyte size. The endogenous productions of T, $E_2$ and 17 ${alpha}-hydroxy$, 20 ${eta}-dihydroprogesterone;(17{alpha}20{eta}OHP)$ were quantified using a radioimmunoassay in the non-precursor group. The endogenous levels of T and $E_2$ were highest in 1.08 to 12-mm oocytes and $17{alpha}20{eta}OHP$ was produced only in 1.90 to 95-mm oocytes. The relationship between oocyte size and steroidogenesis showed that 1.08 to 12-mm oocytes are full vitellogenic following induction of the maturation process. Moreover, $17{alpha}20{eta}OHP$ acts as a maturation inducing hormone in H. otakii.