Objective To investigate the association between CHI3L1 polymorphism and asthma in the Han population of Guangdong,and to explore the clinical values of chitinase-like protein YKL-40 in evaluating disease severity and monitoring the progression of the disease.Methods Total 251 objects were divided into asthma group (n=150)and control group(n=101).The single nucleotide polymorphism (SNP)at CHI3L1 gene was detected with Massarray method. The serum YKL-40 levels, total IgE levels, peripheral blood eosinophil percentage (Eos%)of the obj ects in asthma and control groups were detected. The asthma patients were divied into asthma exacergation group and stable group,and the serum YKL-40 levels were compared.Results The distribution of A/G at rs3806448 of CHI3L1 had significant difference between asthma and control groups (P<0.01 ), and the frequency of A allele at rs3806448 of the patients in asthma group was significantly higher than that in control group (OR= 1.93,95% CI=1.30-2.62,χ2=11.6,P<0.01).The serum YKL-40 levels,total IgE and Eos% of the patients with AA at rs3806448 were higher than those of the patients with GG or AG at rs3806448 (P<0.05);the FEV1% of the patients with AA was lower than those of the patients with GG or AG at rs3806448(P<0.01). The serum YKL-40 level of the patients in asthma group was significantly higher than that in normal control group (P<0.01),and the serum YKL-40 level of the patients in asthma exacergation group was higher than those in asthma stable group and normal control group(P<0.01).The serum YKL-40 level of the patients in asthma group was positively correlated with the peripheral blood Eos% and total IgE level(rEos=0.348,rIgE=0.437,P<0.01), and was negatively correlated with the lung function(r=-0.745,P<0.01). Conclusion The polymorphism of CHI3L1-rs3806448 may correlate with asthma of Han population in Guangdong area.The serum YKL-40 may be a new biomarker to evaluate asthma disease severity and helpful for monitoring illness stage.