Background Cryptosporidium baileyi is the dominant Cryptosporidium species in birds causing emerging health problem in the poultry industry,and is also a model to study biology of Cryptosporidium spp..IL-17(also called IL-17A)is a hallmark pro-inflammatory cytokine of Th17 cells that plays an important role in several human autoimmune diseases and microbial infection disease of many animals,and it may play a role in Cryptosporidium infection.Methods The present study examined the mRNA level of IL-17 and Th17 response relative cytokines in trachea and spleen of C.baileyi-infected chickens at different time points using real-time quantitative PCR(qPCR).Results All examined cytokines in trachea were up-regulated in the infected chickens compared with the uninfected control during C.baileyi infection.Significant increased IL-17 mRNA level in trachea was observed as early as 12 h post infection(pi),peaking at 24 h pi and 10 d pi,and declining thereafter.The transcription levels of IL-17 and Th17 response relative eytokines in spleen were also significantly increased at different time points during the infection.Conclusions IL-17 was indicated to participate in the induction of inflammation during infection of some intracellular protozoan parasites.The results in the present study suggested that IL-17 may play a role in immunity against Cryptosporidium infection,and provided basic information for determining the role of Th17 cell in Cryptosporidium infection.