Free radicals such as nitric oxide (NO) and reactive oxygen species (ROS) are involved in many physiological processes. In humans, there are 5 homologs of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Noxes) that generate superoxide (O 2 -), which can dismute to produce ROS, and play significant roles in innate immunity and cell proliferation. Though Noxes have been identified in vertebrates (humans and fishes) and some insects, there are very few reports investigating Noxes in crustaceans. In the present study, we describe the entire cDNA sequence (4216bp) of Marsupenaeus japonicus (kuruma shrimp) Nox (MjNox) generated using reverse transcriptase-polymerase chain reaction (RT-PCR) and random amplification of cDNA ends (RACE). The open reading frame of MjNox encodes a protein of 1280 amino acids with an estimated mass of 146kDa that has 46.8% sequence homology with the Nox gene of the fruit fly, Drosophila melanogaster. Highly conserved amino acid sequences were observed in the NADPH binding domain. Transcriptional analysis revealed that MjNox mRNA is highly expressed in the lymphoid organ, hepatopancreas and hemocytes of the healthy kuruma shrimp. In the hemocytes, MjNox expression reached its peak 4h after stimulation with either Vibrio penaeicida or poly(I:C) and decreased to its normal level after 12h. This study is the first to identify and clone a Nox family member (MjNox) from a crustacean species. © 2011 Elsevier Ltd.