Background: Dipeptidyl Peptidase I (DPPI) is one of the essential components which initiate chain reaction for triggering the inflammatory response mediated allergic diseases such as asthma. Previous studies have reported that several mutations have been detected within the dipeptidyl peptidase I gene (CTSC) cause Papillon-Lefévre syndrome. It has been suggested that a mutation in this gene could give protection against the inflammatory response in allergic diseases. The aim of this study was to investigate wither the polymorphism (rs217086 (T153I)) in the gene for DPPI may be protective in asthma. Methods: To examine possible associations of DPP1 polymorphism with asthma susceptibility, we performed this study. 341 families with at least two siblings with asthma were genotyped for a CTSC polymorphism using high resolution melting curve analysis. Genetic association analysis was analysed using family based association tests (FBAT) and resultant called genotypes were sequenced. Results: DNA sequence data confirmed all variant genotypes. Analysis by FBAT showed no significant association between this polymorphism and asthma susceptibility or with any of asthma-related phenotypes tested. Conclusions: Our data proved that DPPI does not contribute substantially to susceptibility for asthma. Further studies examining both genotypes and environmental factors will be necessary to elucidate the role of DPPI in the development of allergic diseases.