This study reports on the results of supplementation with iron or multiple micronutrient powders (MNPs) on brain activity measures using resting electroencephalography within a three-arm, double-blind, double-dummy, individual randomized trial in Bangladesh, in which 3,300 eight-month-old children were randomly selected to receive three months of daily iron syrup (12.5 mg iron), MNPs (including 12.5 mg iron), or placebo.