Pups (5 days old) were undernourished by separating them for 14 hr daily from their mothers for 7, 10, 13, 16 and 20 days. The undernourished rats showed significant decrease in body and brain weight, protein and nucleic acid contents at all stages of observation as compared to controls. The activities of SDH and AChE enzymes were decreased significantly after 10 days and onwards in undernourished rat brain. However, maximum decrease in brain protein, nucleic acid contents and enzyme activities was observed during suckling-weaning-transition (20-21 days). Such alterations in enzyme activities may be correlated with the reduced oxidative and neurotransmission function in undernourished developing rat brain.