As a member of the RNase III nucleases family, Dicer1 (Dcr1) protein plays an essential role in the production of microRNAs (miRNAs) and oocyte development. Here, the full‐length cDNA of Nilaparvata lugens Dcr1 (NlDcr1) was firstly cloned and analyzed, and then the function of NlDcr1 gene was investigated by RNAi. The open reading frameof NlDcr1 cDNA was 6,720 bp in length (GenBank Accession no. JX644040), which encoded for a protein of 2,239 amino acids. The NlDcr1 transcripts were present in all developmental stages and tissues investigated. The lowest levels of NlDcr1 expression were found in the first and second instar stage, while the highest in 7‐ and 9 ‐day‐old female adults. The expression levels were relatively higher in fat body, ovary, and midgut. After injecting 100 ng dsRNA of NlDcr1 into female adult, mRNA level of NlDcr1 gene was depleted significantly, and 10 kinds of tested miRNAs levels were downregulated in both whole body and ovary. The oocytes of females treated with dsNlDcr1 were smaller and badly malformed, among which the follicular cell did not develop normally, with unclear boundary between cells. These results suggest that NlDcr1 was crucial for the regulation of oogenesis in telotrophic ovary.