YKL-40 is a member of the mammalian chitinase like protein class of 40 Kda (kilo Dalton) heparin binding glycoprotein. Its name is derived from the protein's molecular weight and three N-terminus amino acids (tyrosine[y], lysine[k] and leucine[l]) (Ober; et al 2008).   YKL-40 is secreted by various cell-types including macrophages, chondrocytes, and some types of cancer cells.  The exact physiological role of YKL-40 is not known, but it has been implicated in cell development, inflammatory disease such as asthma and cancer progression (Francescone; et al 2011). The aim of this study was to investigate whether serum YKL-40 were increased in Asthmatic children and identify its correlation with acute exacerbation, total IgE, blood Eosinophil percentage (EO%) and Pulmonary Function (PF).We measured serum YKL-40 levels, EO%, and serum IgE in 30 children with Asthma as well as in 20 apparently healthy controls from the communities surrounding AL-Salama Hospital, EL-Khobar district, Saudi Arabia. Pulmonary Function (PF) of Asthmatic patients was also measured. Our data showed that the serum YKL-40 was significantly elevated in patients with Asthma (77.66ng/mL) compared with control (55.16ng/mL)  (P=0.001) and when Asthma patients were stratified, serumYKL-40 levels in exacerbation group were significantly higher (83.72 ng/mL) than those in stable Asthmatic group (77.66ng/mL) (P=0.043). In addition, serum YKL-40 was correlated positively with the level of IgE (with r =0.298 and p = 0.018) and EO% (with r = 0.272 and p =0.032) but negatively correlated to pulmonary functions as Forced Expiratory Volume in 1st second (FEV1)(with r =-0.044 and p=0.0001). Thus, we conclude that YKL-40 is found significantly high in the serum of asthmatic children and its level correlates with exacerbation attacks, indicating that high levels of serum YKL-40 may be biological characteristic of the asthma exacerbation.