Bronchial asthma is a common chronic inflammatory disease affecting the airway. Cytokines have a pivotal role in regulation of the immune response, and in development of asthma. Interleukin 33 is a newly discovered member of cytokines, belongs to interleukin 1 family. Previous studies have reported that expression of IL33 is associated with bronchial asthma. This study aimed to evaluate the prevalence of interleukin 33 (IL33) single nucleotide polymorphism (SNP) rs1929992 in asthmatic patients and determine the relation of IL33SNP to IL33 serum level. The Results of RFLP were validated by using sterile distilled water. This study included 100 patients from Egypt, Beni Suef governorate (Upper Egypt) and Mansoura governorate (Delta region), complaining of chronic asthma and 100 control subjects with matched sex and residence. Blood samples from study subjects were used for determination of serum IL33by ELISA and IL33 SNP rs1929992 by PCR-RFLP. There was no significant difference between the proportions of IL33 SNP rs1929992 genotypes in asthma patients and the control group. Allele ‘A’predominates in asthmatics though this did not achieve statistical significance (P= 0.071). IL33 level was compared in the three IL33 SNP rs1929992 genotypes; G/G, G/A, and A/A, and it revealed no significant difference (P= 0.958). The association between IL33 with asthma showed that the log-additive model is the best inheritance model which marks allele ‘A’as the risk allele. In contrast, IL33 serum level was significantly higher in severe asthma than the moderate asthma and the mild type (P< 0.0005). Spearman’s correlation test showed …