This study was carried out to investigate correlationships between serum hormones such as LH, FSH, estradiol-17β and progesterone. and serum components (12 components) obtained from 120 of 3-year-old female rainbow trout (Oncorhynchus mykiss). All data were collected and analysed monthly from March in 1989 to February in 1990. The results obtained in this study were as follows : The correlation between serum LH and BUN during spawning period was highly negative (r=-0.793), while the correlations of LH with creatinine and total protein were high (r=0.887 and 0.688. respectively). Similarly, the relationships of serum FSH with creatinine (r=0.831) and total protein (r=0.709) were significantly highly positive. The concentration of estradiol-17β was highly correlated with creatinine, total protein. and triglycerides. But the relation between serum progesterone and BUN was significantly negative (r=-0.606). Ultimately, three kinds of hormones such as LH, FSH, estradiol-17β in female rainbow trout, seemed to be correlated with serum components associated with vitellogenesis and oogenesis.