1. This report deals with the breeding biology of Emberiza cioides, and is based on the results of field observations from 1965 to 1967 in Nagano, Honshu.<br>2. Several adjacent pairs begin nesting very synchronously between late April and early May.<br>3. The nest is built by female only and is completed by 6 days on the average. Nesting period may be as long as 9 days for some early nesters, but only about 3 days for late breeders.<br>4. The nest is just placed on the ground or twig, not tangled. Female first builds outer parts of nest and goes on to lining. The frequency of carrying lining material is lower than for outer material. Copulation takes place mainly on the ground during lining period.<br>5. When the chicks and eggs are eaten by predators, another nest is attempted at once. Later nests are built at average 29 meters apart from preceding one.<br>6. Most of the nests are found on the ground or in the bushes below 1 meter, and later nests tend to be built off the ground.<br>7. Eggs of a clutch are laid daily in the eary morning (5:00-6:00 A.M.), the average size being 4.4 and decreases with the progress of the breeding season.<br>8. Females begin incubation on the day the last egg is laid, and incubation period is 11.16 days on the average. On and off sessions in daytime are average 58.3 and 22.5min. respectively. Constancy rate of incubation (Skutch 1962) is 67.3%. Feeding to female by the male is not observed either on or near the nest.<br>9. Female mainly broods the chicks about 15min. after each feeding, and does so until the chicks are about 6 days-old.<br>10. The period of nestling is about 11 days. In this period, the male and female, take the equal share of feeding. The frequency of feeding per one chick is 0.45 (average) per hour, but a little less in the early and later periods.<br>11. After leaving nest chicks are shared by parents for feeding and remain from 25 to 29 days in the home-range. After the family flock have broken up the female at once begins nest-building for the second brood.<br>12. In Otagiri, Nagano, the most important factor of population regulation of Emberiza cioides in breeding reason is a low hatching rate caused by predators. Breeding success per eggs laid is 20-35%.