【Objective】To determine and compare the level of serum YKL-40 at acute stage of cerebral infarction and to investigate the relationship among the levels of serum YKL-40 and different classification of acute ischemic stroke. 【Methods】Serum YKL-40 levels were measured by enzyme immunoassay in 91 patients with cerebral infarction (within 48 hours on admission) and 34 healthy controls. The relationship among the YKL-40 and clinical classification and the etiologic subtype of stroke were investigated. 【Results】The levels of serum YKL-40 were significantly increased in patients with cerebral infarction than the normal control subjects (P<0.001). The levels of serum YKL-40 in large infarct group and TACI group and CE group were significantly higher than those in other groups according to different classification criteria. 【Conclusions】Serum YKL-40 level elevated after ischemic stroke and was related to infarct size and the etiology. The serum YKL-40 might be a new biological marker to predict the severity and prognosis of ischemic stroke. Key words: cerebral infarction; YKL-40; classification