To understand the sequence features and phylogeny of interleukin 17 (IL-17) in sweet fish (Plecoglossus altivelis), and its correlation to Listonella anguillarum infection, the cDNA sequence of IL-17C was cloned from P. altivelis by RACE-PCR, and the expression changes of different tissues were detected after L. anguillarum infection by real-time quantitative PCR (qRT-PCR). The full length of P. altivelis IL-17C cDNA was 1 087 bp including a 534 bp ORF and seven 3'UTR instability motifs (ATTTA), and it encoded 177 amino acids with eight conservation cysteine (Cys) and a 19 amino acids N-terminal signal peptide. Phylogenetic tree analysis showed that the same IL-17 subtype homologue from different species gathered together, and the P. altivelis IL-17C was clustered in one group with other vertebrate IL-17C. Multiple sequence alignment and phylogenetic analysis showed that P. altivelis IL-17C has higher similarity to Oncorhynchus mykiss IL-17C1 (40.72%) and O. mykiss IL-17C2 (34.04%). In healthy P. altivelis, IL-17C mRNA expression was detected in heart, liver, spleen, head kidney, gill, brain, muscle and intestine, high expression was shown in gill and head kidney. After L. anguillarum infection, the expression of IL-17C increased 9.17 folds in liver at 8 hpi (hours post infection) and 6.69 folds in spleen at 4 hpi compared to the control group. IL-17C gene is closely related to the pathogenic bacteria infection of P. altivelis, and it may play an important role in inflammatory immune response.