Abstract: Macrobrachium rosenbergii and Drosophila melanogaster all belong to the phylum arthropoda. Previous works in Drosophila melanogaster had revealed that autophagy is closely related to immunity, whereas there are few reports on the autophagy of shrimp. As a molecular marker of autophagy, microtubule-associated protein 1 light chain 3（Lc3）, a homologue of the autophagy gene Atg8, is localized in autophagosome membranes after processing. In this study, the c DNA sequence of MrLc3 a of Macrobrachium rosenbergii was cloned by RACE-PCR and the expression of MrLc3 a in major tissues was detected by RT-qPCR. Also the changes in the expression of MrLc3 a and immune gene Relish were studied under the normal and Vibrio parahaemolyticus infected condition. The results showed that the full-length c DNA of MrLc3 a gene consists of 653 base pairs（bp）, including 195 bp 5’ noncoding region（UTR）, 80 bp 3’ non-coding region（UTR） and 378 bp open reading frame（ORF）. It encodes a protein of 126 amino acids. The amino acid sequence alignment showed that the Lc3 a of Macrobrachium rosenbergii shared high sequence identity with Lc3 a of Penaeus vannamei and its phylogenetic analysis was consistent with the traditional morphological classification. The RT-qPCR results showed that the MrLc3 a gene was expressed in all tissues, with a higher expression in brain, gills, and stomach, and a lower expression in hepatopancreas and gonads. MrLc3 a m RNA and Relish mRNA transcript level in hepatopancreas changed significantly after exposure to Vibrio parahaemolyticus, showing a tendency of rising first then decreasing, which suggested that MrLc3 a was involved in the immune response through autophagy.