The developmental electroencephalogram (EEG) was recorded from 64 beagles to make a map on the normal EEG in relation to the change of age and the state of consciousness, and to establish the criterion of evaluation on the abnormal EEG. Montages used were four rhinal reference recordings (LF-R, RF-R, LO-R, RO-R) and four bipolar ones (LF-RF, LO-RO, LF-LO, RF-RO). Rhythmic waves which were occasionally seen at the 1st postnatal day increased with days of age and appeared constantly in the 7th postnatal day. The wakefulness and sleep were distinguished in the EEG of two weeks of age. It was revealed that the EEG on the 5th week could be classified into wakefulness, light sleep, middle sleep and deep sleep, because prototypes of all wave patterns or wave forms such as desynchronizations, rhythmic waves of 8-13 Hz, humps, primitive spindles and slow waves below 3 Hz occurred in this age. These waves increased in their amplitudes up to 10-12 weeks of age and then gradually decreased in them. It was also demonstrated that the maturation of the EEG in the dog may occur in 20-30 weeks of age, when it is evaluated from the changes of the EEG due to the state of consciousness.