This study demonstrates the use of an oligonucleotide DNA array to analyze the expression profiles of microRNAs (miRNAs) during brain development. The array was designed to target 44 mature miRNAs expressed in the brain and revealed precise regulation of miRNA expression at various developmental stages. Approximately 20% of the probed miRNAs showed significant changes in expression during normal brain development. Specifically, miR-9 and miR-131, which are dysregulated in presenilin-1 null mice with severe brain developmental defects, were identified. Northern blot validation confirmed the differential expression of these miRNAs. The arrays also revealed that miRNAs are distributed to translating polyribosomes in primary neurons, suggesting their role in modulating translation. Bioinformatic analysis of developmentally regulated miRNAs suggested potential mRNA targets, including calcineurin Aβ, Id2, and DNA helicase SMBP2. The study highlights the utility of oligonucleotide arrays in studying miRNA expression and regulation in various biological and pathobiological contexts.This study demonstrates the use of an oligonucleotide DNA array to analyze the expression profiles of microRNAs (miRNAs) during brain development. The array was designed to target 44 mature miRNAs expressed in the brain and revealed precise regulation of miRNA expression at various developmental stages. Approximately 20% of the probed miRNAs showed significant changes in expression during normal brain development. Specifically, miR-9 and miR-131, which are dysregulated in presenilin-1 null mice with severe brain developmental defects, were identified. Northern blot validation confirmed the differential expression of these miRNAs. The arrays also revealed that miRNAs are distributed to translating polyribosomes in primary neurons, suggesting their role in modulating translation. Bioinformatic analysis of developmentally regulated miRNAs suggested potential mRNA targets, including calcineurin Aβ, Id2, and DNA helicase SMBP2. The study highlights the utility of oligonucleotide arrays in studying miRNA expression and regulation in various biological and pathobiological contexts.