This experiment was undertaken to investigate the effects of prolonged feeding of domestic rapeseed meal on some economical characters and thyroid function in the egg type chicken breeder female. Three hundred and thirty three chicks of 2 week-old commercial breed (Ishii Z22) were divided into three groups of one hundred eleven (6 males and 105 females) each, and rapeseed meal was fed for 40 weeks at levels of 0 (control), 8 and 13 percent of the diets. The metabolizable energy, protein and lysine levels of treated diet were equal with control, and every nutrient content in each diets r4as approximately equivalent to NRC recommendation. The results obtained in this experiment were summarized as follows: 1. Up to 20 weeks of age, there were no significant differences between treatments on either mortality, body weight gain, feed consumption or feed conversion rate. Considering these results, it was presumed that the use of domestic rapeseed meal at the 13 percent level of rations was safe for rearing period of laying type breeder. 2. In Iaying period, viability, final (42 weeks of age) body weight, feed consumption and body weight gain per 1㎏ feed intake were lower with the rapeseed meal diets than with the control diet. However, no significant differences between treatments in these characters except feed intake were noted. 3. Rapeseed meal feeding for rearing period did not effect on the sexual maturity and egg weight at 50 percent production. But the continuous feeding for laying period significantly lowered egg production and egg size as compared with control feeding. This result indicated that special regard would be paid to the use of native rapeseed meal at 8 percent level over in laying ration. 4. There was no difference in feed consumption per 10 eggs, however, for the feed requirement per 1㎏ egg production 13 percent level rapeseed meal fed birds resulted in slightly higher than the other two groups. 5. fertility and hatchability were similar in the eggs from the birds fed control and rapeseed meal diets throughout the experiment. However, the chicks from the eggs laid by the rapeseed meal-fed birds were slightly smaller at hatching those of the birds fed control diet. And rapeseed meal in the breeder ration resulted in significant increase in the thyroid weights of progeny at hatching. 6. Rapeseed meal in the ration resulted in significant increases in the weights of the thyroid glands relative to total body weights. The increase in thyroid size was greater with the higher level of rapeseed meal in the diet and with the longer period of feeding rapeseed meal diet. 7. The sizes of follicles and epithelial cells in the thyroid glands of birds were also increased significantly by feeding of rapeseed meal diets. As time of treatment progresses, however, the sizes of those were drawed near to that of control. The glandular enlargement in this instance was found to be caused by the increased number of follicles. 8. The concentration of cholesterol in the blood serum of birds was significantly elevated by the feeding of rapeseed meal diets. But at 6 and 9 weeks after feeding rapeseed meal, the elevated serum cholesterol concentrations were reverted to almost normal level. This result suggests that the thyroid apparently reaches physiological equilibrium at 6 and 9 weeks after feeding of rapeseed meal diets, therefore goitrin in rapeseed meal may not be detrimental to the normal egg production of the laying hen. 9. There were no significant differences between treatments on the values of erythrocyte counts and hemoglobin contents. Considering this result, it was presumed that the use of domestic rapeseed meal about 13 percent level of ration did not decrease the secretion race of thyroid hormone enough to reach anaemia.