OBJECTIVE To determine postnatal maturation of findings in the electroencephalogram (EEG) of calves and estimate the degree of electrophysiologic activity, using power spectrum and cross-correlation analyses of the EEG. METHODS 10 clinically normal Japanese Black calves ranging in age from 1 to 10 weeks. METHODS EEG were recorded at various stages of consciousness. Power spectrum and cross-correlation analyses were applied to a relaxed state EEG. RESULTS After the second week of age, rhythmic waves with frequencies of 6 to 9 Hz (alpha rhythm-like pattern) appeared in the EEG during the relaxed state, and were recorded in the occipital and vertex areas; duration of appearance was < 30 seconds. By use of power spectrum analysis, power distribution of the 7.5- to 10-Hz frequency band in the occipital area significantly increased after the sixth week. The highest frequency (18 to 30 Hz) band increased in the frontal and occipital areas after the seventh week. Normalized cross-correlation coefficients at 0 time shift were > 0.6 throughout the experimental period. The normalized cross-correlation coefficients obtained from caudal interhemispheric sites increased after the second week, and were significantly greater than those in rostral sites. CONCLUSIONS Developmental changes in the EEG of calves during the first 10 weeks could be characterized by appearance of the alpha rhythm-like pattern and increase of the power distributions of the 7.5- to 10-Hz and 18- to 30-Hz frequency bands, which might be a useful indicator for estimating brain activity in young calves and as standard data for evaluating abnormal brain activity in calves.