The purpose of the study was the estimation of the changes in the activity of 20 individual sRNA amino acyl synthetases in the newborn, 12th, 30th, 48th and 180th days old rabbit brain. The investigations showed that the highest enzyme activity was found in the pH 5 fraction obtained from the CNS of newborn rabbits. In the further period of brain’s development there was a decline in the activity of amino acyl sRNA synthetases beginning from the 12th day of extrauterine life and continuing until the animals were 48 days old, when the activity approximated that measured in the adult rabbit brain. The activity of these enzymes in the developing brain was higher in the cerebral cortex than in the white matter.