C-type lectins are important immune molecules that participate in crustacean defense response. The present work reports a novel C-type lectin (PcLec6) from the red swamp crayfish Procambarus clarkii. PcLec6 encodes a single-peptide protein of 385 amino acids, which include a C-type lectin domain (CTLD) and a serine-rich region. PcLec6 expression in lymph organ and gills was up-regulated after bacterial challenge by Vibrio alginolyticus or white spot syndrome virus (WSSV). Recombinant full-length PcLec6 or its CTLD proteins were used for the functional analyses. Results showed that these two proteins had the capacity to bind to carbohydrates and bacteria. Both the full-length PcLec6 and CTLD facilitated the bacterial clearance, but only full-length PcLec6 protected crayfish from WSSV infection. Furthermore, PcLec6 regulated the expression of ALF genes. These results suggest that PcLec6 is involved in the innate immune response of crayfish against both bacterial and viral pathogens.