Objective To determine the association of articular cartilage (AC) levels of YKL-40 with osteoarthritis (OA) at different stages of symptomatic severity in patients with knee OA.Methods 42 patients with knee OA were recruited into this study.The radiographic disease severity of OA was assessed by the Kellgren-Lawrence (K-L) grading system.11 patients with non knee OA were selected as normal control group.AC levels of YKL -40 were explored by immunohistochemical method.Symptomatic severity was determined using Western Ontario and McMaster Universities Arthritis Index (WOMAC) scores from OA patients.Results YKL-40 levels in AC were positively related to WOMAC pain,function scores and total scores.WOMAC stiffness scores did not correlated with YKL-40 concentrations in AC.The correlation between AC YKL-40 levels and WOMAC scores was further analyzed by multinomial logistic regression.Multiple regression analysis showed that the correlation between AC YKL-40 levels and WOMAC scores was still significant after adjusting for other confounding factors.AC YKL-40 levels were significantly correlated with K-L grading in patients with knee OA.Conclusions YKL-40 in AC can be used as a potential biomarker for assessing the symptomatic severity of OA.